feat(sprint7): Phase 2 — Info Board (Schwarzes Brett)

Backend:
- V13 Flyway migration: info_board_posts, post_attachments, post_read_status tables
- InfoBoardPost entity with category enum (EVENT, RULE, GENERAL, MAINTENANCE)
- PostAttachment entity (table created, upload deferred to later)
- PostReadStatus entity with composite key (post_id, member_id)
- InfoBoardPostRepository with paginated queries + unread count
- InfoBoardService: CRUD, pin/archive, mark-as-read, notification dispatch
- InfoBoardController: admin CRUD + portal read/unread endpoints
- Integration with NotificationService and AuditService

Frontend:
- info-board.ts service with React Query hooks for all endpoints
- Admin Info Board page at /info-board with create dialog, filters, pin/archive/delete
- Navigation: added 'Schwarzes Brett' to admin sidebar
- i18n: added infoBoard.* keys to de.json and en.json
- Fixed pre-existing prettier issues in notification-compose.ts
- Fixed BufferSource type issue in push-subscription.ts

cannamanage-frontend/e2e/test-results/.last-run.json

@@ -1,4 +1,4 @@
 {
   "status": "passed",
   "failedTests": []
-}
+}