Add Android background geolocation with notification error handling

Add flutter_background_geolocation for background location tracking on Android.
Service automatically sends coordinates to server when app is in background.
Error messages are shown as system notifications using flutter_local_notifications.

lib/main.dart

@@ -6,6 +6,7 @@ import 'providers/map_provider.dart';
 import 'providers/share_provider.dart';
 import 'screens/login_screen.dart';
 import 'screens/map_screen.dart';
+import 'services/background_geo_service.dart';
 import 'services/settings_service.dart';
 
 void main() async {
@@ -13,13 +14,20 @@ void main() async {
   final settings = SettingsService();
   await settings.initialize();
   ApiConfig.setBaseUrl(settings.baseUrl);
-  runApp(MyApp(settingsService: settings));
+  final bgGeo = BackgroundGeoService();
+  await bgGeo.init();
+  runApp(MyApp(settingsService: settings, bgGeo: bgGeo));
 }
 
 class MyApp extends StatelessWidget {
   final SettingsService settingsService;
+  final BackgroundGeoService bgGeo;
 
-  const MyApp({super.key, required this.settingsService});
+  const MyApp({
+    super.key,
+    required this.settingsService,
+    required this.bgGeo,
+  });
 
   @override
   Widget build(BuildContext context) {
@@ -29,6 +37,7 @@ class MyApp extends StatelessWidget {
         ChangeNotifierProvider(create: (_) => AuthProvider()),
         ChangeNotifierProvider(create: (_) => MapProvider()),
         ChangeNotifierProvider(create: (_) => ShareProvider()),
+        Provider.value(value: bgGeo),
       ],
       child: MaterialApp(
         title: 'Family Safety',