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

frontend/vitest.config.ts

@@ -4,5 +4,17 @@ export default defineConfig({
   test: {
     environment: "jsdom",
     include: ["src/**/*.test.ts"],
+    coverage: {
+      provider: "v8",
+      reporter: ["text", "text-summary"],
+      include: ["src/**/*.ts"],
+      exclude: ["src/**/*.test.ts"],
+      thresholds: {
+        statements: 40,
+        branches: 30,
+        functions: 30,
+        lines: 40,
+      },
+    },
   },
 });