Show Google sign-in diagnostics

lib/google_calendar_page.dart

@@ -147,6 +147,8 @@ class _AccountsPageState extends State<AccountsPage> {
 
     try {
       if (!initialized) {
+        final configuredClientId = await _loadGoogleServerClientId();
+        runtimeServerClientId = configuredClientId?.trim();
         await _ensureGoogleInitialized();
         initialized = true;
       }
@@ -155,13 +157,15 @@ class _AccountsPageState extends State<AccountsPage> {
       await _loadGoogleCalendars(promptIfNecessary: true);
     } catch (error) {
       if (!mounted) return;
-      setState(() {
+      final friendlyMessage = _friendlyGoogleError(
-        loadingCalendars = false;
-        statusMessage = _friendlyGoogleError(
         'Google bejelentkez\u00e9s nem siker\u00fclt',
         error,
       );
+      setState(() {
+        loadingCalendars = false;
+        statusMessage = friendlyMessage;
       });
+      await _showGoogleErrorDialog(friendlyMessage);
     }
   }
 
@@ -176,6 +180,27 @@ class _AccountsPageState extends State<AccountsPage> {
     return '$prefix: $raw';
   }
 
+  Future<void> _showGoogleErrorDialog(String message) async {
+    if (!mounted) return;
+    await showDialog<void>(
+      context: context,
+      builder: (context) => AlertDialog(
+        title: const Text('Google bel\u00e9p\u00e9s nem indult el'),
+        content: Text(
+          '$message\n\n'
+          'A v\u00e1rt m\u0171k\u00f6d\u00e9s az, hogy a Google saj\u00e1t bel\u00e9p\u00e9si/enged\u00e9lyez\u00e9si ablaka ny\u00edlik meg. '
+          'Ehhez az appnak el\u0151re regisztr\u00e1lt Google konfigur\u00e1ci\u00f3 kell, \u00e9s az eszk\u00f6z\u00f6n Google Play Services / Google fi\u00f3k is sz\u00fcks\u00e9ges.',
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.pop(context),
+            child: const Text('Rendben'),
+          ),
+        ],
+      ),
+    );
+  }
+
   Future<void> _ensureGoogleInitialized() async {
     final clientId = runtimeServerClientId;
     if (clientId == null || clientId.isEmpty) {