android: allow existing scheduled work to be replaced

Without this we end up in situations where changes to constraints
are not propagated immediately because of pre-scheduled work that
is retained until it has run.

android/src/main/kotlin/dev/msfjarvis/claw/android/MainActivity.kt

@@ -48,7 +48,7 @@ class MainActivity : ComponentActivity() {
       WorkManager.getInstance(this@MainActivity)
         .enqueueUniquePeriodicWork(
           "updateSavedPosts",
-          ExistingPeriodicWorkPolicy.KEEP,
+          ExistingPeriodicWorkPolicy.REPLACE,
           postUpdateWorkRequest,
         )
     }