chore: import upstream snapshot with attribution

validation/example-validate.md

@@ -0,0 +1,61 @@
+---
+description: Comprehensive validation for this codebase
+---
+
+# Validate Codebase
+
+> **Example generated validation command** for a React + FastAPI + PostgreSQL app
+
+## Phase 1: Linting
+!`cd frontend && npm run lint`
+!`cd backend && ruff check src/`
+
+## Phase 2: Type Checking
+!`cd frontend && npx tsc --noEmit`
+!`cd backend && mypy src/`
+
+## Phase 3: Style Checking
+!`cd frontend && npm run format:check`
+!`cd backend && black --check src/`
+
+## Phase 4: Unit Testing
+!`cd frontend && npm test -- --coverage`
+!`cd backend && pytest tests/unit -v --cov=src`
+
+## Phase 5: End-to-End Testing
+
+### Setup
+!`docker-compose up -d`
+!`timeout 60 bash -c 'until curl -f http://localhost:8000/health; do sleep 2; done'`
+
+### Frontend E2E (Playwright)
+!`cd frontend && npx playwright test`
+
+**Tests:**
+- User registration → email verification → login
+- Create item → edit item → delete item
+- Search and filter functionality
+- Error handling and validation
+- All main user workflows
+
+### Backend E2E (API + Database)
+
+**Test all API endpoints:**
+!`curl -X POST http://localhost:8000/api/auth/register -d '{"email":"test@test.com","password":"Test123!"}'`
+!`TOKEN=$(curl -X POST http://localhost:8000/api/auth/login -d '{"email":"test@test.com","password":"Test123!"}' | jq -r '.token')`
+!`curl http://localhost:8000/api/items -H "Authorization: Bearer $TOKEN"`
+!`curl -X POST http://localhost:8000/api/items -H "Authorization: Bearer $TOKEN" -d '{"name":"Test"}'`
+
+**Verify database:**
+!`docker exec postgres psql -U user -d db -c "SELECT COUNT(*) FROM users;"`
+!`docker exec postgres psql -U user -d db -c "SELECT * FROM items WHERE name='Test';"`
+
+**Test error handling:**
+!`curl -w "%{http_code}" http://localhost:8000/api/items/invalid-id` # Should be 404
+!`curl -w "%{http_code}" http://localhost:8000/api/admin -H "Authorization: Bearer $TOKEN"` # Should be 403
+
+### Cleanup
+!`docker-compose down -v`
+
+## Summary
+All validation passed! Ready for deployment.