UI rework: modal dialogs, inline lab editing, manual creation, content management

- Dashboard: real stats (groups, students, labs, average grade), labs/groups
  summary lists, no placeholder tile
- Lab page: view + edit combined — metadata form in modal, condition rendered
  as markdown, per-level variant tables with add/edit/delete dialogs,
  level rename/delete, student level/variant selectors with group filter
- Labs list: create-lab dialog with manual level entry (code; title lines)
- Groups: create-group dialog, add-student dialog (auto password, toast card)
- Content: public /learn reader is the single place; admin buttons (new
  article with chapter/section create-or-select, rename/delete chapters and
  sections, move articles between sections, import zip) appear for admins;
  removed separate 'Контент' admin section
- Buttons use btn classes instead of nav-link
- Favicon: generated SVG book icon
- Security: CSRF synchronizer token interceptor (replaced spring-security in
  web which broke logback under nested jars), session regenerated on login,
  hardened session cookie, gateway actuator limited to health,info
- Jackson 3: nullable-safe request DTOs for labs (FAIL_ON_NULL_FOR_PRIMITIVES)
- academic: POST /labs (manual create with levels), level add/rename/delete,
  content chapters/sections CRUD, article create/move/delete endpoints

web/src/main/resources/templates/learn/article.html

@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<html lang="ru" xmlns:th="http://www.thymeleaf.org" th:replace="~{fragments/base :: layout(~{::title}, ~{::#content})}">
+<head><title th:text="${article.title} + ' — LMS'">Статья</title></head>
+<body>
+<div id="content">
+    <nav class="text-sm mb-4">
+        <a th:href="@{/learn}" class="nav-link">Материалы</a>
+        <span class="nav-sep mx-2">/</span>
+        <a th:href="@{/learn/{c}(c=${article.chapterSlug})}" class="nav-link" th:text="${article.chapterTitle}">Глава</a>
+        <span class="nav-sep mx-2">/</span>
+        <a th:href="@{/learn/{c}/{s}(c=${article.chapterSlug}, s=${article.sectionSlug})}" class="nav-link"
+           th:text="${article.sectionTitle}">Раздел</a>
+    </nav>
+    <h1 class="page-title" th:text="${article.title}">Статья</h1>
+    <div class="card card-body md-body" th:utext="${article.bodyHtml}"></div>
+</div>
+</body>
+</html>

web/src/main/resources/templates/learn/index.html

@@ -0,0 +1,195 @@
+<!DOCTYPE html>
+<html lang="ru" xmlns:th="http://www.thymeleaf.org" th:replace="~{fragments/base :: layout(~{::title}, ~{::#content})}">
+<head><title>Материалы — LMS</title></head>
+<body>
+<div id="content">
+    <div class="flex items-center justify-between gap-4 mb-6">
+        <h1 class="page-title">Учебные материалы</h1>
+        <div th:if="${currentUser != null and currentUser.admin}" class="flex gap-2">
+            <button class="btn btn-primary" type="button" onclick="openModal('modal-new-article')">+ Статья</button>
+            <button class="btn btn-secondary" type="button" onclick="openModal('modal-import')">Импорт zip</button>
+            <button class="btn btn-secondary" type="button" onclick="openModal('modal-manage')">Главы и разделы</button>
+        </div>
+    </div>
+    <div th:if="${notice}" class="alert alert-success" th:text="${notice}"></div>
+    <div th:if="${error}" class="alert alert-error" th:text="${error}"></div>
+
+    <div th:if="${tree == null || #lists.isEmpty(tree.chapters)}" class="card card-body text-muted">
+        Материалы ещё не добавлены.
+    </div>
+    <div th:each="chapter : ${tree.chapters}" class="card mb-4" th:id="|chapter-${chapter.id}|">
+        <div class="card-body">
+            <div class="flex items-center justify-between gap-4 mb-4">
+                <h2 class="section-title" th:text="${chapter.title}">Глава</h2>
+                <div th:if="${currentUser != null and currentUser.admin}" class="flex gap-2">
+                    <button class="btn btn-secondary btn-sm" type="button"
+                            th:onclick="openModal('modal-rename-chapter-'+${chapter.id})">Переименовать</button>
+                    <form th:action="@{/admin/content/chapters/{id}/delete(id=${chapter.id})}" method="post"
+                          onsubmit="return confirm('Удалить главу со всеми разделами и статьями?')">
+                        <input type="hidden" name="_csrf" th:value="${csrfToken}">
+                        <button class="btn btn-danger btn-sm" type="submit">Удалить</button>
+                    </form>
+                </div>
+            </div>
+            <div th:each="section : ${chapter.sections}" class="mt-4"
+                 th:id="|section-${section.id}|">
+                <div class="flex items-center justify-between gap-4">
+                    <h3 class="group-title">
+                        <a th:href="@{/learn/{c}/{s}(c=${chapter.slug}, s=${section.slug})}" th:text="${section.title}">Раздел</a>
+                    </h3>
+                    <div th:if="${currentUser != null and currentUser.admin}" class="flex gap-2">
+                        <button class="btn btn-secondary btn-sm" type="button"
+                                th:onclick="openModal('modal-rename-section-'+${section.id})">Переименовать</button>
+                        <button class="btn btn-secondary btn-sm" type="button"
+                                th:onclick="openModal('modal-move-'+${section.id})">Перенести статьи</button>
+                        <form th:action="@{/admin/content/sections/{id}/delete(id=${section.id})}" method="post"
+                              onsubmit="return confirm('Удалить раздел со всеми статьями?')">
+                            <input type="hidden" name="_csrf" th:value="${csrfToken}">
+                            <button class="btn btn-danger btn-sm" type="submit">Удалить</button>
+                        </form>
+                    </div>
+                </div>
+                <ul class="list-pad text-sm">
+                    <li th:each="article : ${section.articles}" class="flex items-center gap-2">
+                        <a th:href="@{/learn/{c}/{s}/{a}(c=${chapter.slug}, s=${section.slug}, a=${article.slug})}"
+                           th:text="${article.title}">Статья</a>
+                        <th:block th:if="${currentUser != null and currentUser.admin}">
+                            <button class="btn btn-secondary btn-sm" type="button"
+                                    th:onclick="openModal('modal-edit-article-'+${article.id})">Править</button>
+                            <form class="inline-form" th:action="@{/admin/content/articles/{id}/delete(id=${article.id})}" method="post"
+                                  onsubmit="return confirm('Удалить статью?')">
+                                <input type="hidden" name="_csrf" th:value="${csrfToken}">
+                                <button class="btn btn-danger btn-sm" type="submit">✕</button>
+                            </form>
+                        </th:block>
+                    </li>
+                    <li th:if="${#lists.isEmpty(section.articles)}" class="text-muted">Статей пока нет</li>
+                </ul>
+            </div>
+            <p th:if="${#lists.isEmpty(chapter.sections)}" class="text-sm text-muted">Разделов пока нет</p>
+        </div>
+    </div>
+</div>
+
+<dialog id="modal-import" class="modal">
+    <div class="modal-header">
+        <h2 class="modal-title">Импорт материалов (zip)</h2>
+        <button class="modal-close" type="button" onclick="closeModal('modal-import')">✕</button>
+    </div>
+    <div class="modal-body">
+        <form class="form-stack" th:action="@{/admin/content/import}" method="post" enctype="multipart/form-data">
+            <input type="hidden" name="_csrf" th:value="${csrfToken}">
+            <p class="text-sm text-muted">
+                Структура: <code class="code">chapters/01-глава/01-раздел/01-статья.md</code>, картинки в <code class="code">assets/</code>.
+            </p>
+            <div><label class="label" for="file">Архив</label>
+                <input class="input" id="file" name="file" type="file" accept=".zip" required></div>
+            <button class="btn btn-primary" type="submit">Импортировать</button>
+        </form>
+    </div>
+</dialog>
+
+<dialog id="modal-new-article" class="modal">
+    <div class="modal-header">
+        <h2 class="modal-title">Новая статья</h2>
+        <button class="modal-close" type="button" onclick="closeModal('modal-new-article')">✕</button>
+    </div>
+    <div class="modal-body">
+        <form class="form-stack" th:action="@{/admin/content/articles/create}" method="post">
+            <input type="hidden" name="_csrf" th:value="${csrfToken}">
+            <div><label class="label" for="naChapter">Глава (можно создать новую)</label>
+                <div class="inline-form w-full">
+                    <select class="input" id="naChapter" name="chapterId" th:if="${tree != null}">
+                        <option th:each="chapter : ${tree.chapters}" th:value="${chapter.id}" th:text="${chapter.title}">—</option>
+                    </select>
+                    <span class="text-muted">или</span>
+                    <input class="input" name="newChapterTitle" placeholder="Новая глава">
+                </div>
+            </div>
+            <div><label class="label" for="naSection">Раздел (можно создать новый)</label>
+                <input class="input" id="naSection" name="newSectionTitle" placeholder="Новый раздел"></div>
+            <div><label class="label" for="naTitle">Заголовок статьи</label>
+                <input class="input" id="naTitle" name="title" required></div>
+            <div><label class="label" for="naBody">Текст (markdown)</label>
+                <textarea class="input" id="naBody" name="bodyMd" rows="10"></textarea></div>
+            <button class="btn btn-primary" type="submit">Создать</button>
+        </form>
+    </div>
+</dialog>
+
+<th:block th:each="chapter : ${tree?.chapters ?: {}}">
+    <dialog th:id="|modal-rename-chapter-${chapter.id}|" class="modal">
+        <div class="modal-header">
+            <h2 class="modal-title">Переименовать главу</h2>
+            <button class="modal-close" type="button" th:onclick="closeModal('modal-rename-chapter-'+[[${chapter.id}]])">✕</button>
+        </div>
+        <div class="modal-body">
+            <form class="form-stack" th:action="@{/admin/content/chapters/{id}/rename(id=${chapter.id})}" method="post">
+                <input type="hidden" name="_csrf" th:value="${csrfToken}">
+                <div><label class="label">Название</label>
+                    <input class="input" name="title" th:value="${chapter.title}" required></div>
+                <button class="btn btn-primary" type="submit">Сохранить</button>
+            </form>
+        </div>
+    </dialog>
+    <th:block th:each="section : ${chapter.sections}">
+        <dialog th:id="|modal-rename-section-${section.id}|" class="modal">
+            <div class="modal-header">
+                <h2 class="modal-title">Переименовать раздел</h2>
+                <button class="modal-close" type="button" th:onclick="closeModal('modal-rename-section-'+[[${section.id}]])">✕</button>
+            </div>
+            <div class="modal-body">
+                <form class="form-stack" th:action="@{/admin/content/sections/{id}/rename(id=${section.id})}" method="post">
+                    <input type="hidden" name="_csrf" th:value="${csrfToken}">
+                    <div><label class="label">Название</label>
+                        <input class="input" name="title" th:value="${section.title}" required></div>
+                    <button class="btn btn-primary" type="submit">Сохранить</button>
+                </form>
+            </div>
+        </dialog>
+        <dialog th:id="|modal-move-${section.id}|" class="modal">
+            <div class="modal-header">
+                <h2 class="modal-title">Перенести статьи из раздела</h2>
+                <button class="modal-close" type="button" th:onclick="closeModal('modal-move-'+[[${section.id}]])">✕</button>
+            </div>
+            <div class="modal-body">
+                <form class="form-stack" th:action="@{/admin/content/sections/{id}/delete(id=${section.id})}" method="post">
+                    <input type="hidden" name="_csrf" th:value="${csrfToken}">
+                    <p class="text-sm text-muted">Укажите раздел, в который перенести статьи, затем подтвердите удаление раздела.</p>
+                    <div><label class="label">Перенести в раздел</label>
+                        <select class="input" name="moveTo" th:if="${tree != null}">
+                            <th:block th:each="ch2 : ${tree.chapters}">
+                                <optgroup th:label="${ch2.title}">
+                                    <option th:each="s2 : ${ch2.sections}"
+                                            th:if="${s2.id != section.id}"
+                                            th:value="${s2.id}" th:text="${ch2.title} / ${s2.title}">—</option>
+                                </optgroup>
+                            </th:block>
+                        </select></div>
+                    <button class="btn btn-primary" type="submit">Перенести и удалить раздел</button>
+                </form>
+            </div>
+        </dialog>
+    </th:block>
+</th:block>
+
+<th:block th:each="a : ${articles}">
+    <dialog th:id="|modal-edit-article-${a.id}|" class="modal">
+        <div class="modal-header">
+            <h2 class="modal-title">Правка статьи</h2>
+            <button class="modal-close" type="button" th:onclick="closeModal('modal-edit-article-'+[[${a.id}]])">✕</button>
+        </div>
+        <div class="modal-body">
+            <form class="form-stack" th:action="@{/admin/content/articles/{id}/save(id=${a.id})}" method="post">
+                <input type="hidden" name="_csrf" th:value="${csrfToken}">
+                <div><label class="label">Заголовок</label>
+                    <input class="input" name="title" th:value="${a.title}" required></div>
+                <div><label class="label">Текст (markdown)</label>
+                    <textarea class="input" name="bodyMd" rows="14" th:text="${a.bodyMd}"></textarea></div>
+                <button class="btn btn-primary" type="submit">Сохранить</button>
+            </form>
+        </div>
+    </dialog>
+</th:block>
+</body>
+</html>

web/src/main/resources/templates/learn/section.html

@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html lang="ru" xmlns:th="http://www.thymeleaf.org" th:replace="~{fragments/base :: layout(~{::title}, ~{::#content})}">
+<head><title th:text="${section.title} + ' — LMS'">Раздел</title></head>
+<body>
+<div id="content">
+    <a th:href="@{/learn}" class="nav-link">← Все материалы</a>
+    <h1 class="page-title mt-4" th:text="${section.title}">Раздел</h1>
+    <p class="text-sm text-muted mb-6">Глава: <span th:text="${chapter.title}">—</span></p>
+    <div class="card card-flush">
+        <table>
+            <thead><tr><th>Статья</th></tr></thead>
+            <tbody>
+            <tr th:each="article : ${section.articles}">
+                <td><a th:href="@{/learn/{c}/{s}/{a}(c=${chapter.slug}, s=${section.slug}, a=${article.slug})}"
+                       th:text="${article.title}">—</a></td>
+            </tr>
+            <tr th:if="${#lists.isEmpty(section.articles)}"><td class="empty">Статей пока нет.</td></tr>
+            </tbody>
+        </table>
+    </div>
+</div>
+</body>
+</html>