Fix blank stations page - add auth gate guard in App.tsx

ROOT CAUSE: Race condition where StationsPage renders before auth
token is ready, causing DOM state mismatch.

Timeline of the bug:
1. Auth0 sets isAuthenticated=true
2. App renders StationsPage before isAuthInitialized=true
3. useSavedStations hook is disabled (enabled: false)
4. Google Maps loads and manipulates DOM
5. Auth token finally acquired, isAuthInitialized=true
6. Component re-renders with query now enabled
7. React tries to remove DOM nodes already removed by Google Maps
8. NotFoundError: removeChild fails

SOLUTION: Add isAuthGateReady check in App.tsx before rendering
protected routes. Show "Initializing session..." until auth gate is
fully initialized.

Changes:
- Import useIsAuthInitialized hook in App.tsx
- Call hook in App component
- Add guard check after isAuthenticated check
- Show loading UI if authenticated but auth gate not ready
- Add debug logs to track render flow

Now the page won't render until BOTH:
1. isAuthenticated=true (Auth0)
2. isAuthInitialized=true (our token gate)

This prevents the race condition that causes the removeChild DOM error.

🤖 Generated with Claude Code

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

frontend/src/App.tsx

@@ -6,6 +6,7 @@ import React, { useState, useEffect, useTransition, useCallback, lazy } from 're
 import { useQueryClient } from '@tanstack/react-query';
 import { Routes, Route, Navigate } from 'react-router-dom';
 import { useAuth0 } from '@auth0/auth0-react';
+import { useIsAuthInitialized } from './core/auth/auth-gate';
 import { motion, AnimatePresence } from 'framer-motion';
 import { ThemeProvider } from '@mui/material/styles';
 import CssBaseline from '@mui/material/CssBaseline';
@@ -237,7 +238,9 @@ const AddVehicleScreen: React.FC<AddVehicleScreenProps> = ({ onBack, onAdded })
 
 function App() {
   const { isLoading, isAuthenticated, user } = useAuth0();
+  const isAuthGateReady = useIsAuthInitialized();
   const [_isPending, startTransition] = useTransition();
+  console.log('[DEBUG App] Render check - isLoading:', isLoading, 'isAuthenticated:', isAuthenticated, 'isAuthGateReady:', isAuthGateReady);
 
   // Initialize data synchronization
   const { prefetchForNavigation } = useDataSync();
@@ -380,6 +383,32 @@ function App() {
     );
   }
 
+  // Wait for auth gate to be ready before rendering protected routes
+  // This prevents a race condition where the page renders before the auth token is ready
+  if (!isAuthGateReady) {
+    console.log('[DEBUG App] Auth gate not ready yet, showing loading state');
+    if (mobileMode) {
+      return (
+        <ThemeProvider theme={md3Theme}>
+          <CssBaseline />
+          <Layout mobileMode={true}>
+            <div className="flex items-center justify-center h-64">
+              <div className="text-slate-500">Initializing session...</div>
+            </div>
+          </Layout>
+        </ThemeProvider>
+      );
+    }
+    return (
+      <ThemeProvider theme={md3Theme}>
+        <CssBaseline />
+        <div className="flex items-center justify-center min-h-screen">
+          <div className="text-lg">Initializing session...</div>
+        </div>
+      </ThemeProvider>
+    );
+  }
+
   // Mobile app rendering
   if (mobileMode) {
     return (