feat: Add task execution callback registration to BackgroundTaskService and update geofence dispatcher to use it

apps/mobile/packages/core/lib/src/services/device/background_task/background_task_service.dart

@@ -55,4 +55,16 @@ class BackgroundTaskService extends BaseDeviceService {
   Future<void> cancelAll() async {
     return action(() => Workmanager().cancelAll());
   }
+
+  /// Registers the task execution callback for the background isolate.
+  ///
+  /// Must be called inside the top-level callback dispatcher function.
+  /// The [callback] receives the task name and optional input data, and
+  /// must return `true` on success or `false` on failure.
+  void executeTask(
+    Future<bool> Function(String task, Map<String, dynamic>? inputData)
+        callback,
+  ) {
+    Workmanager().executeTask(callback);
+  }
 }