test: add unit/integration/E2E test suites, fix create_session bug, update docs

- Unit tests: test_session.py (27), test_error_kb.py (24), test_agent.py hardened
- Integration tests: test_api_integration.py (25) with FastAPI TestClient
- E2E tests: main-flows.spec.ts (8) with Playwright + API mocking
- Bug fix: backend/session.py create_session() missing session_id parameter
- Config: frontend/playwright.config.ts, npm run test:e2e
- Docs: update CLAUDE.md v9, .gitignore for test artifacts/eval reports

frontend/package.json

@@ -6,13 +6,15 @@
   "scripts": {
     "dev": "vite",
     "build": "vue-tsc -b && vite build",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test:e2e": "playwright test"
   },
   "dependencies": {
     "pinia": "^3.0.4",
     "vue": "^3.5.34"
   },
   "devDependencies": {
+    "@playwright/test": "^1.60.0",
     "@types/node": "^24.12.3",
     "@vitejs/plugin-vue": "^6.0.6",
     "@vue/tsconfig": "^0.9.1",