feat: Phase 2+3 frontend coverage — responsive + accessibility tests + CI threshold

- Viewer accessibility: 5 tests (aria-labels, aria-expanded, label association, alert role)
- Viewer responsive: 3 tests (chat-collapsed, CSS grid, now-playing aria-live)
- Admin accessibility: 3 tests (nav aria-label, aria-current, focusability)
- Admin responsive: 2 tests (tab visibility, essential tabs)
- Coverage: vitest v8 provider, 40% stmt/lines, 30% branches/funcs
- CI: test:coverage step between lint and build
- Total: 44 frontend tests (31 + 13 new)
- Updated TODO.md (Phase 2+3 done), DONE.md, MEMORY.md

.gitea/workflows/ci.yml

@@ -26,6 +26,9 @@ jobs:
       - name: Lint Frontend
         run: cd frontend && npm run lint
 
+      - name: Test Frontend with Coverage
+        run: cd frontend && npm run test:coverage
+
       - name: Build Frontend
         run: cd frontend && npm run build