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/utils/constants.dart

@@ -1,6 +1,5 @@
 class AppConstants {
   static const String appName = 'Family Safety';
-  static const String defaultMapsApiKey = 'YOUR_MAPS_API_KEY';
   
   // Default coordinates (Moscow)
   static const double defaultLatitude = 55.7558;