Phase 2+5: lab submissions and student lab flow

- progress: submissions table+V4; SubmissionService (deadline-gated submit,
  unlimited resubmits, per-student history, zip download); files on disk
  data/submissions/{student}/{lab}/{seq}/
- student API: POST submit (multipart), GET me submissions, download; admin
  GET lab submissions + admin download (zip pack)
- progress enrich(): labId in MeAssignment; web DTO aligned
- web: /student dashboard (avg/best/worst cards), /student/labs cards,
  /student/labs/{id}: condition md, variant block, submit form, history;
  'Лабораторные' link in nav for students
- admin: submissions column on lab assignment table + download link
- fixed long-standing template bug: broken @{} expression (missing }) in
  admin/lab and student/lab

web/src/main/resources/templates/student/lab.html

@@ -0,0 +1,61 @@
+<!DOCTYPE html>
+<html lang="ru" xmlns:th="http://www.thymeleaf.org" th:replace="~{fragments/base :: layout(~{::title}, ~{::#content})}">
+<head><title th:text="|ЛР ${lab.number} — LMS|">Лабораторная</title></head>
+<body>
+<div id="content">
+    <a th:href="@{/student/labs}" class="nav-link">← Лабораторные</a>
+    <div class="flex flex-wrap items-center justify-between gap-4 mt-4 mb-2">
+        <h1 class="page-title" th:text="|Лабораторная работа ${lab.number}. ${lab.title}|">ЛР</h1>
+        <div class="flex gap-2 text-sm">
+            <span th:if="${grade != null}" class="badge badge-ok">Оценка: <span th:text="${grade}"></span></span>
+            <span th:if="${assignment != null}" class="badge badge-warn">Вариант <span class="font-mono" th:text="${assignment.variantNumber}"></span></span>
+        </div>
+    </div>
+    <p class="text-sm text-muted mb-6" th:if="${deadlineMsk}">Срок сдачи: <span th:text="${deadlineMsk}"></span> МСК</p>
+
+    <div th:if="${notice}" class="alert alert-success" th:text="${notice}"></div>
+    <div th:if="${error}" class="alert alert-error" th:text="${error}"></div>
+
+    <h2 class="section-title">Условие лабораторной</h2>
+    <div class="card card-body md-body mb-6" th:utext="${descriptionHtml}"></div>
+
+    <th:block th:if="${assignment != null}">
+        <h2 class="section-title">Ваш вариант <span class="font-mono" th:text="${assignment.variantNumber}"></span>
+            <span class="text-muted text-sm" th:if="${assignment.levelTitle}" th:text="|(${assignment.levelTitle})|"></span></h2>
+        <div class="card card-body md-body mb-6" th:utext="${statementHtml}"></div>
+    </th:block>
+    <div th:if="${assignment == null}" class="card card-body mb-6">
+        <p class="text-muted">Ваш вариант ещё не распределён. Дождитесь, пока преподаватель распределит варианты.</p>
+    </div>
+
+    <h2 class="section-title">Сдача работы</h2>
+    <div class="card form-card form-stack mb-4">
+        <form th:action="@{/student/labs/{id}/submit(id=${lab.id})}" method="post" enctype="multipart/form-data" class="form-stack">
+            <input type="hidden" name="_csrf" th:value="${csrfToken}">
+            <p class="text-sm text-muted">zip‑архив или исходники (.c/.h). Пока не истёк срок, можно пересывать столько раз, сколько нужно — засчитывается последняя попытка.</p>
+            <div><input class="input" name="files" type="file" multiple required></div>
+            <div th:if="${canSubmit}">
+                <button class="btn btn-primary" type="submit">Отправить решение</button>
+            </div>
+            <div th:unless="${canSubmit}" class="alert alert-warning">Срок сдачи истёк — отправка закрыта.</div>
+        </form>
+    </div>
+
+    <h3 class="group-title">История сдач</h3>
+    <div class="card card-flush">
+        <table>
+            <thead><tr><th>Попытка</th><th>Когда (МСК)</th><th>Файлы</th><th></th></tr></thead>
+            <tbody>
+            <tr th:each="s : ${submissions}">
+                <td th:text="${s.seq}">1</td>
+                <td class="text-muted" th:text="${#strings.replace(s.createdAt, 'T', ' ')}"></td>
+                <td class="font-mono text-sm"><span th:each="f : ${s.files}" th:text="${f}"></span></td>
+                <td><a class="btn btn-secondary btn-sm" th:href="'/student/submissions/' + ${s.id} + '/download'">Скачать</a></td>
+            </tr>
+            <tr th:if="${#lists.isEmpty(submissions)}"><td colspan="4" class="empty">Вы ещё ничего не сдавали.</td></tr>
+            </tbody>
+        </table>
+    </div>
+</div>
+</body>
+</html>