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.

services/identity-service/src/main/resources/db/migration/V3__login_attempts.sql

@@ -0,0 +1,7 @@
+-- Счётчик неудачных входов для экспоненциальной задержки (защита от перебора паролей).
+
+CREATE TABLE login_attempts (
+    login           varchar(64) PRIMARY KEY,
+    failures        integer     NOT NULL DEFAULT 0,
+    last_failure_at timestamptz NOT NULL DEFAULT now()
+);