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/static/favicon.svg

@@ -1,7 +1,4 @@
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32">
-  <rect x="2" y="2" width="28" height="28" rx="6" fill="#6366f1"/>
-  <path d="M9 8v13h5l-1.5 3H6V8z" fill="#eef2ff"/>
-  <path d="M23 8v13h-5l1.5 3h5V8z" fill="#c7d2fe"/>
-  <path d="M11 9c2-1.5 4-1.5 5 0 1-1.5 3-1.5 5 0v10c-2-1.5-4-1.5-5 0-1-1.5-3-1.5-5 0z" fill="#ffffff"/>
-  <path d="M16 9v10" stroke="#6366f1" stroke-width="1"/>
+  <rect x="1" y="1" width="30" height="30" rx="8" fill="#7a2333"/>
+  <path d="M11.5 7.5h4v13.2h8.2v3.8h-12.2z" fill="#fdfcf9"/>
 </svg>