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.

libs/common-http/build.gradle.kts

@@ -7,6 +7,8 @@ dependencies {
 
     api(libs.springWeb)
     api(libs.springBootAutoconfigure)
+    // spring-tx нужен для обработчика DataIntegrityViolationException в LmsExceptionHandler.
+    api("org.springframework:spring-tx")
     // Kotlin-модуль Jackson: корректная десериализация data-классов со значениями по умолчанию.
     api(libs.jacksonModuleKotlin)
 }