feat: add frontend test infrastructure and fix CI workflow

- Fix pnpm version mismatch in test_next_server.yml (8 → auto-detect 10)
- Add concurrency group to cancel stale CI runs
- Remove redundant setup-node step
- Update jest.config.js for jsdom + tsx support
- Add meetingStatusBatcher integration test (3 tests)
- Extract createMeetingStatusBatcher factory for testability

www/package.json

@@ -62,9 +62,13 @@
   "author": "Andreas <andreas@monadical.com>",
   "license": "All Rights Reserved",
   "devDependencies": {
+    "@testing-library/dom": "^10.4.1",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
     "@types/jest": "^30.0.0",
     "@types/react": "18.2.20",
     "jest": "^30.1.3",
+    "jest-environment-jsdom": "^30.2.0",
     "openapi-typescript": "^7.9.1",
     "prettier": "^3.0.0",
     "ts-jest": "^29.4.1"