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.

ios/Runner/Info.plist

@@ -59,5 +59,14 @@
 	<false/>
 	<key>NSMotionUsageDescription</key>
 	<string>MeshCore SAR needs access to the compass to show your heading direction on the map</string>
+	<key>UIBackgroundModes</key>
+	<array>
+		<string>location</string>
+		<string>fetch</string>
+	</array>
+	<key>BGTaskSchedulerPermittedIdentifiers</key>
+	<array>
+		<string>dev.flutter.background.refresh</string>
+	</array>
 </dict>
 </plist>