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/app/schemas/auth.py

@@ -0,0 +1,36 @@
+from pydantic import BaseModel
+from typing import Optional
+
+
+class LoginRequest(BaseModel):
+    email: str
+    password: str
+
+
+class LoginResponse(BaseModel):
+    access_token: str
+    token_type: str = "bearer"
+    user: "UserInfo"
+
+
+class UserInfo(BaseModel):
+    id: str
+    email: str
+    name: str
+    role: Optional[str] = None
+    department_id: Optional[str] = None
+    is_system_admin: bool = False
+
+
+class TokenPayload(BaseModel):
+    sub: str
+    email: str
+    role: Optional[str] = None
+    department_id: Optional[str] = None
+    is_system_admin: bool = False
+    exp: int
+    iat: int
+
+
+# Update forward reference
+LoginResponse.model_rebuild()