Refactor: Remove background task management and related hooks

- Deleted `useBackgroundTasks.ts` hook and its associated logic for managing background tasks.
- Removed `backgroundTaskManager.ts` service and all related task definitions and registrations.
- Cleaned up `Podfile.lock` and `package.json` to remove unused dependencies related to background tasks.
- Updated iOS project files to eliminate references to removed background task components.
- Added new background fetch identifier in `Info.plist` for future use.

app.json

@@ -68,8 +68,7 @@
             "./assets/sounds/notification.wav"
           ]
         }
-      ],
-      "expo-background-task"
+      ]
     ],
     "experiments": {
       "typedRoutes": true