Redesign B3 bordeaux + finish lab-page rework

- Lab page is now read-only with a settings screen for levels/variants;
  variant issuance moved to a large modal on the group page (assign-fragment).
- Header: bordeaux logo and 2px accent underline, bordeaux login/logout/theme
  buttons; smaller radii across the UI; filled secondary/danger buttons.
- Includes prior agent work (login backoff, no-cache pages, API timeouts,
  content tweaks) and fixes (variant usage Map.values, import order).
- Bump static asset version to v=9.

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

@@ -33,7 +33,7 @@
                 </h3>
                 <p class="text-sm" th:text="${c.title}">—</p>
                 <div class="flex flex-wrap gap-2 mt-2 text-sm">
-                    <span th:if="${c.variantNumber}" class="badge badge-warn">вариант <span class="font-mono" th:text="${c.variantNumber}"></span></span>
+                    <span th:if="${c.variantNumber}" class="badge">вариант <span class="font-mono" th:text="${c.variantNumber}"></span></span>
                     <span th:if="${c.submissionSeq}" class="badge badge-ok">сдано (попытка <span th:text="${c.submissionSeq}">1</span>)</span>
                     <span th:unless="${c.submissionSeq}" class="badge badge-warn">не сдано</span>
                     <span th:if="${c.grade}" class="badge badge-ok">оценка: <span th:text="${c.grade}"></span></span>