fix(app): 修改设备加载任务执行周期

- 将 LoadDeviceWorker 的执行周期从 30秒改为 30 分钟- 优化了后台任务的执行频率，减少不必要的资源消耗

app/src/main/java/com/example/retention/MainActivity.java

@@ -202,7 +202,7 @@ public class MainActivity extends AppCompatActivity {
 
   private void startLoadWork() {
     PeriodicWorkRequest workRequest = new PeriodicWorkRequest.
-        Builder(LoadDeviceWorker.class, 30, TimeUnit.SECONDS)
+        Builder(LoadDeviceWorker.class, 30, TimeUnit.MINUTES)
         .setInitialDelay(0, TimeUnit.SECONDS)
         .addTag(WORK_TAG)
         .build();