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>

frontend/src/contexts/AuthContext.tsx

@@ -0,0 +1,74 @@
+import { createContext, useContext, useState, useEffect, ReactNode } from 'react'
+import { authApi, User, LoginRequest } from '../services/api'
+
+interface AuthContextType {
+  user: User | null
+  isAuthenticated: boolean
+  loading: boolean
+  login: (data: LoginRequest) => Promise<void>
+  logout: () => Promise<void>
+}
+
+const AuthContext = createContext<AuthContextType | undefined>(undefined)
+
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const [user, setUser] = useState<User | null>(null)
+  const [loading, setLoading] = useState(true)
+
+  useEffect(() => {
+    // Check for existing token on mount
+    const token = localStorage.getItem('token')
+    const storedUser = localStorage.getItem('user')
+
+    if (token && storedUser) {
+      try {
+        setUser(JSON.parse(storedUser))
+      } catch {
+        localStorage.removeItem('token')
+        localStorage.removeItem('user')
+      }
+    }
+    setLoading(false)
+  }, [])
+
+  const login = async (data: LoginRequest) => {
+    const response = await authApi.login(data)
+    localStorage.setItem('token', response.access_token)
+    localStorage.setItem('user', JSON.stringify(response.user))
+    setUser(response.user)
+  }
+
+  const logout = async () => {
+    try {
+      await authApi.logout()
+    } catch {
+      // Ignore errors on logout
+    } finally {
+      localStorage.removeItem('token')
+      localStorage.removeItem('user')
+      setUser(null)
+    }
+  }
+
+  return (
+    <AuthContext.Provider
+      value={{
+        user,
+        isAuthenticated: !!user,
+        loading,
+        login,
+        logout,
+      }}
+    >
+      {children}
+    </AuthContext.Provider>
+  )
+}
+
+export function useAuth() {
+  const context = useContext(AuthContext)
+  if (context === undefined) {
+    throw new Error('useAuth must be used within an AuthProvider')
+  }
+  return context
+}