feat(authentication): implement frontend authentication system

- Created auth and user types (T10)
- Implemented API client with token handling (T11)
- Built AuthContext with JWT decoding (T12)
- Added ProtectedRoute component (T13)
- Created LoginPage, RegisterPage, DashboardPage (T14-T16)
- Updated App.tsx with routing and auth provider (T17)
- Added Dockerfile, nginx.conf for frontend deployment (T18-T19)
- Updated docker-compose.yml to include frontend service (T20)
- Updated .gitignore to exclude frontend build artifacts (T21)
- Removed unused App.css (T22)

Refs #2

Frontend/src/components/ProtectedRoute.tsx

@@ -0,0 +1,14 @@
+import { Navigate, Outlet } from 'react-router-dom';
+import { useAuth } from '../hooks/useAuth';
+
+const ProtectedRoute = () => {
+  const { isAuthenticated } = useAuth();
+
+  if (!isAuthenticated) {
+    return <Navigate to="/login" replace />;
+  }
+
+  return <Outlet />;
+};
+
+export default ProtectedRoute;