feat(frontend): add React dashboard with TypeScript

Add modern React frontend to replace Streamlit dashboard:
- Vite build system with TypeScript
- Tailwind CSS for styling
- Component structure in src/
- Production Dockerfile with nginx
- Development server on port 5173

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/components/ProtectedRoute.tsx

@@ -0,0 +1,30 @@
+import { Navigate, useLocation } from 'react-router-dom';
+import { useAuth } from '../context/AuthContext';
+
+interface ProtectedRouteProps {
+  children: React.ReactNode;
+  requireAdmin?: boolean;
+}
+
+export function ProtectedRoute({ children, requireAdmin = false }: ProtectedRouteProps) {
+  const { isAuthenticated, isAdmin, isLoading } = useAuth();
+  const location = useLocation();
+
+  if (isLoading) {
+    return (
+      <div className="min-h-screen bg-gradient-to-br from-bg-dark to-indigo-950 flex items-center justify-center">
+        <div className="animate-spin rounded-full h-12 w-12 border-t-2 border-b-2 border-primary"></div>
+      </div>
+    );
+  }
+
+  if (!isAuthenticated) {
+    return <Navigate to="/login" state={{ from: location }} replace />;
+  }
+
+  if (requireAdmin && !isAdmin) {
+    return <Navigate to="/analysis" replace />;
+  }
+
+  return <>{children}</>;
+}