Refactor web UI: CSS classes only, no inline styles; fix footer; add full lab1.zip

- Replace all inline style= with reusable CSS classes
- Add layout classes: page, page-header, page-main, page-footer
- Fix footer at bottom via flex column + flex:1 on main
- Remove jsessionid from static resource URLs
- Create lab1-full.zip with 30 variants from PDF metodichka
- All templates use CSS var classes for light/dark theme

web/src/main/resources/templates/error.html

@@ -1,13 +1,12 @@
 <!DOCTYPE html>
-<html lang="ru" xmlns:th="http://www.thymeleaf.org"
-      th:replace="~{fragments/base :: layout(~{::title}, ~{::#content})}">
+<html lang="ru" xmlns:th="http://www.thymeleaf.org" th:replace="~{fragments/base :: layout(~{::title}, ~{::#content})}">
 <head><title>Ошибка — LMS</title></head>
 <body>
 <div id="content">
-    <div style="max-width:28rem;margin:0 auto;text-align:center;">
-        <p style="font-size:4rem;font-weight:700;color:var(--c-text-muted);opacity:0.3;" th:text="${status}">500</p>
-        <p style="margin-top:1rem;" th:text="${message}">Что-то пошло не так</p>
-        <a class="btn btn-secondary" style="margin-top:1.5rem;display:inline-flex;" th:href="@{/}">На главную</a>
+    <div class="container-sm text-center">
+        <p class="stat-value text-muted opacity-30" th:text="${status}">500</p>
+        <p class="mt-4" th:text="${message}">Что-то пошло не так</p>
+        <a class="btn btn-secondary mt-6" th:href="@{/}">На главную</a>
     </div>
 </div>
 </body>