docs: add comprehensive testing guide with flaky test documentation

- Create docs/TESTING.md with full testing documentation
- Document 3 flaky test suites with exact locations and workarounds
- Update README.md with accurate test status (~348-349 passing)
- Add troubleshooting guide for race conditions
- Include CI/CD considerations and future improvements

Key sections:
- Running tests (commands, environment, configuration)
- Flaky tests: matching-algorithm, ratings-stats-flow, events
- Known issues & fixes applied (migrations, constraints, config)
- Debugging strategies and test isolation tips

README.md

@@ -198,20 +198,43 @@ docker compose exec backend npm run cli -- users:list --limit 20
 
 ## 📊 Test Coverage
 
-**Backend: 351/351 tests passing - 100% ✅** (73% overall coverage)
+**Backend: ~348-349 passing, ~5-6 flaky, 11 skipped** (365 total tests)
 
-### Test Suites
-- **Matching Algorithm**: 19/19 integration tests
-  - Fundamentals, collision detection, limits, fairness, edge cases
-- **Ratings & Stats Flow**: 9/9 E2E tests
-  - Atomic updates, race prevention, idempotency
+### Test Status
+- ✅ **20/23 test suites stable** - Consistently passing
+- ⚠️ **3/23 test suites flaky** - Pass individually, may fail in full suite (race conditions)
+- ⏭️ **11 tests skipped** - Socket.IO server setup required (3), outdated auth tests (2), rate limiting (1)
+
+### Stable Test Suites
+- **Matching Algorithm**: 19/19 tests (flaky in full suite - run individually)
+- **Ratings & Stats Flow**: 9/9 tests (flaky in full suite - run individually)
 - **Matching Runs Audit**: 6/6 tests
-  - origin_run_id tracking, sequential runs, filtering
 - **Incremental Matching**: 5/5 tests
 - **Recording Stats Integration**: 6/6 tests
 - **WebRTC Signaling**: 12/12 tests
-- **WebRTC API**: 9/9 tests (Cloudflare TURN integration, fallbacks, authentication)
+- **WebRTC API**: 9/9 tests
 - **Socket.IO**: 12/12 tests
+- **Authentication**: 24/24 tests
+- **Dashboard**: 12/12 tests
+- **Users**: 23/25 tests (2 skipped - endpoints are public)
+- **Matches**: 24/24 tests
+- **Events**: 55/55 tests (flaky in full suite - run individually)
+- **And 7 more...**
+
+### Flaky Tests (Known Issues)
+See [docs/TESTING.md](docs/TESTING.md) for detailed analysis of:
+- `matching-algorithm.test.js` - Race conditions in concurrent runs
+- `ratings-stats-flow.test.js` - Database state dependencies
+- `events.test.js` - Cleanup interference between tests
+
+**Workaround:** Run flaky tests individually when needed:
+```bash
+docker compose exec backend npm test -- matching-algorithm.test.js  # ✅ 19/19
+docker compose exec backend npm test -- ratings-stats-flow.test.js  # ✅ 9/9
+docker compose exec backend npm test -- events.test.js              # ✅ 55/55
+```
+
+**Documentation:** See [docs/TESTING.md](docs/TESTING.md) for comprehensive testing guide
 - **API Routes**: Full CRUD coverage (auth, events, matches, dashboard, webrtc)
 
 ### Code Coverage Highlights
@@ -272,6 +295,7 @@ spotlightcam/
     ├── ARCHITECTURE.md        # Technical implementation details
     ├── DEPLOYMENT.md          # Production deployment guide
     ├── MONITORING.md          # Operations & monitoring
+    ├── TESTING.md             # Testing guide & flaky test documentation
     ├── TESTING_MATCHING_RATINGS.md  # Comprehensive test documentation
     ├── WEBRTC_TESTING_GUIDE.md      # WebRTC testing guide
     ├── GOOGLE_ANALYTICS_SETUP.md    # GA4 integration guide
@@ -371,6 +395,7 @@ docker compose exec backend npm run cli -- matches:list --limit 20 --status acce
 **Main documentation:**
 - `docs/TODO.md` - Active tasks, security audit, roadmap
 - `docs/ARCHITECTURE.md` - Technical details, WebRTC flow, API endpoints
+- `docs/TESTING.md` - **Testing guide & flaky test troubleshooting** ⭐
 - `docs/TESTING_MATCHING_RATINGS.md` - Comprehensive test documentation (45 tests)
 - `docs/DEPLOYMENT.md` - Production deployment guide
 - `docs/MONITORING.md` - Operations and monitoring