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/App.tsx

@@ -0,0 +1,32 @@
+import { Routes, Route, Navigate } from 'react-router-dom'
+import { useAuth } from './contexts/AuthContext'
+import Login from './pages/Login'
+import Dashboard from './pages/Dashboard'
+import ProtectedRoute from './components/ProtectedRoute'
+
+function App() {
+  const { isAuthenticated, loading } = useAuth()
+
+  if (loading) {
+    return <div className="container">Loading...</div>
+  }
+
+  return (
+    <Routes>
+      <Route
+        path="/login"
+        element={isAuthenticated ? <Navigate to="/" /> : <Login />}
+      />
+      <Route
+        path="/"
+        element={
+          <ProtectedRoute>
+            <Dashboard />
+          </ProtectedRoute>
+        }
+      />
+    </Routes>
+  )
+}
+
+export default App