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/.env.example

@@ -0,0 +1,22 @@
+# Database
+MYSQL_HOST=mysql.theaken.com
+MYSQL_PORT=33306
+MYSQL_USER=A060
+MYSQL_PASSWORD=your_password_here
+MYSQL_DATABASE=db_A060
+
+# Redis
+REDIS_HOST=localhost
+REDIS_PORT=6379
+REDIS_DB=0
+
+# JWT
+JWT_SECRET_KEY=generate-a-random-secret-key-here
+JWT_ALGORITHM=HS256
+JWT_EXPIRE_MINUTES=15
+
+# External Auth API
+AUTH_API_URL=https://pj-auth-api.vercel.app
+
+# System Admin
+SYSTEM_ADMIN_EMAIL=ymirliu@panjit.com.tw