feat: Implement background location tracking service

- Removed existing app icons from the asset catalog.
- Added new `Contents.json` for asset catalog.
- Updated `Info.plist` to include background modes and task scheduler identifiers.
- Exposed BLE service in `ConnectionProvider` for background tracking.
- Enhanced `MapTab` to support background location tracking with new service.
- Added `BackgroundLocationService` to manage location updates in the background.
- Updated `SettingsScreen` to allow users to configure GPS update distance and toggle background tracking.
- Implemented functionality to send location updates via BLE in `MeshCoreBleService`.
- Updated dependencies in `pubspec.yaml` for background service support.
- Adjusted `TileCacheService` to ensure ObjectBox is initialized only once.

pubspec.yaml

@@ -55,10 +55,6 @@ dependencies:
   geolocator: ^14.0.2
   flutter_compass: ^0.8.0
 
-  # Utilities
-  intl: ^0.20.2
-  collection: ^1.18.0
-
   # File handling
   file_picker: ^8.1.4
   share_plus: ^10.1.3
@@ -70,6 +66,9 @@ dependencies:
   # Package info
   package_info_plus: ^8.1.2
 
+  # Background services
+  flutter_background_service: ^5.0.13
+
 dev_dependencies:
   flutter_test:
     sdk: flutter