feat: more easter eggs + version checking

lib/views/bar/bar_screen_view.dart

@@ -108,6 +108,34 @@ class _BarScreenViewState extends State<BarScreenView> {
     );
   }
 
+  void _showUpdateRequired(String message) {
+    final l10n = AppLocalizations.of(context);
+    showDialog<void>(
+      context: context,
+      builder: (dialogContext) => AlertDialog(
+        title: Text(l10n.appUpdateRequired),
+        content: SelectableText(
+          message.isEmpty
+              ? l10n.appUpdateRequiredDescription
+              : '${l10n.appUpdateRequiredDescription}\n\n$message',
+        ),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.of(dialogContext).pop(),
+            child: Text(l10n.close),
+          ),
+          FilledButton(
+            onPressed: () {
+              Navigator.of(dialogContext).pop();
+              context.push('/settings');
+            },
+            child: Text(l10n.update),
+          ),
+        ],
+      ),
+    );
+  }
+
   void _logout() {
     context.read<PinLockViewModel>().lock();
     context.read<AdminPinViewModel>().lock();
@@ -167,6 +195,16 @@ class _BarScreenViewState extends State<BarScreenView> {
               icon: const Icon(Icons.cloud_off_rounded),
             ),
           ],
+          if (context.watch<RemoteSyncViewModel>().updateRequired
+              case final message?) ...[
+            const SizedBox(width: 6),
+            IconButton(
+              tooltip: l10n.appUpdateRequired,
+              color: Theme.of(context).colorScheme.error,
+              onPressed: () => _showUpdateRequired(message),
+              icon: const Icon(Icons.system_update_rounded),
+            ),
+          ],
           // A failing sync is otherwise invisible: the bar keeps working
           // offline while nothing from the website arrives
           if (context.watch<RemoteSyncViewModel>().lastError