feat: implement user authentication module

- Backend (FastAPI):
  - External API authentication (pj-auth-api.vercel.app)
  - JWT token validation with Redis session storage
  - RBAC with department isolation
  - User, Role, Department models with pjctrl_ prefix
  - Alembic migrations with project-specific version table
  - Complete test coverage (13 tests)

- Frontend (React + Vite):
  - AuthContext for state management
  - Login page with error handling
  - Protected route component
  - Dashboard with user info display

- OpenSpec:
  - 7 capability specs defined
  - add-user-auth change archived

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/requirements.txt

@@ -0,0 +1,16 @@
+fastapi==0.109.0
+uvicorn[standard]==0.27.0
+sqlalchemy==2.0.25
+pymysql==1.1.0
+cryptography==42.0.0
+alembic==1.13.1
+redis==5.0.1
+python-jose[cryptography]==3.3.0
+passlib[bcrypt]==1.7.4
+python-dotenv==1.0.0
+httpx==0.26.0
+pydantic==2.5.3
+pydantic-settings==2.1.0
+pytest==7.4.4
+pytest-asyncio==0.23.3
+pytest-cov==4.1.0