Add Android support with configurable server URL and location permissions

- Add shared_preferences for persisting server URL
- Add SettingsService and PlatformService
- Add server URL input field on non-web platforms
- Make ApiConfig baseUrl configurable at runtime
- Add Android location permissions (ACCESS_FINE/COURSE_LOCATION, INTERNET)
- Request location permission on login and map init
- Fix geo_id type: use String instead of int (UUID format)
- Align share_service with API spec: remove unique_id, use share_id only
- Fix watch endpoint response: last_update instead of created_at
- Add error handling with SnackBars for geo operations
- Wrap login screen in SingleChildScrollView for keyboard handling
- Update map tile layer with userAgentPackageName for OSM

lib/config/api.dart

@@ -1,14 +1,20 @@
 class ApiConfig {
-  static final String baseUrl = Uri.base.origin;
-  
+  static String _baseUrl = 'https://family-safety.onrender.com/api';
+
+  static String get baseUrl => _baseUrl;
+
+  static void setBaseUrl(String url) {
+    _baseUrl = url.endsWith('/') ? url.substring(0, url.length - 1) : url;
+  }
+
   // Auth endpoints
-  static final String loginUrl = '$baseUrl/login';
-  static final String regUrl = '$baseUrl/reg';
-  
+  static String get loginUrl => '$baseUrl/login';
+  static String get regUrl => '$baseUrl/reg';
+
   // Geo endpoints
-  static final String geoUrl = '$baseUrl/geo';
-  
+  static String get geoUrl => '$baseUrl/geo';
+
   // Share endpoints
-  static final String shareUrl = '$baseUrl/share';
-  static final String watchUrl = '$baseUrl/watch';
-}
+  static String get shareUrl => '$baseUrl/share';
+  static String get watchUrl => '$baseUrl/watch';
+}