fix(android): throttle UPnP extend with 50ms delay per successful AddURIToQueue

Closes Scribe #611. The 2026-06-04 logcat showed 33 consecutive AddURIToQueue failures clustered at ~10ms intervals once the burst hit offset 39 -- characteristic of Sonos's burst-add rate-limit. 50ms between successful adds adds ~5s to the 100-track background extension but eliminates the burst rejection. Next reproduction with the SOAP fault detail logging (audit commit c5b326c6) will confirm the fault code if any tracks still fail.

android/app/src/main/java/com/fabledsword/minstrel/player/output/OutputPickerController.kt

@@ -19,6 +19,7 @@ import com.fabledsword.minstrel.player.output.upnp.UpnpDiscoveryController
 import com.fabledsword.minstrel.player.output.upnp.bareUdn
 import dagger.hilt.android.qualifiers.ApplicationContext
 import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
@@ -372,6 +373,13 @@ class OutputPickerController @Inject constructor(
                 if (outcome.isSuccess) {
                     consecutiveFailures = 0
                     succeeded += 1
+                    // Throttle the burst so we don't tickle Sonos's burst-add
+                    // rejection -- logcat 2026-06-04 showed 33 consecutive
+                    // failures clustered at ~10ms intervals once offset 39 was
+                    // reached, which looks like a rate-limit kicking in. The
+                    // delay is small enough that extending 100 tracks adds
+                    // only ~5s to background work that's already async.
+                    delay(EXTEND_THROTTLE_MS)
                 } else {
                     consecutiveFailures += 1
                     val e = outcome.exceptionOrNull()
@@ -423,5 +431,6 @@ class OutputPickerController @Inject constructor(
 
     private companion object {
         const val EXTEND_ABORT_AFTER_FAILURES = 3
+        const val EXTEND_THROTTLE_MS = 50L
     }
 }