fix: tear down nest session on host Close the Room

The host-leave confirmation dialog's Close the Room button only called
finish(), relying on VM.onCleared() to release the AudioRecord. That
runs late in the destroy lifecycle, so the system mic-in-use indicator
stayed lit while the activity was queued for destruction.

Adds NestViewModel.leave(), which mirrors onCleared() (sets closed,
runs both teardowns with finalCleanup=true so closes route through
cleanupScope/GlobalScope and survive Activity destruction). Wires it
into the Close the Room callback only — the Just Leave and non-host
Leave paths are unchanged per request.

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/viewmodels/NestViewModel.kt

@@ -545,6 +545,24 @@ class NestViewModel(
         teardown(targetState = ConnectionUiState.Idle, finalCleanup = false)
     }
 
+    /**
+     * User-driven leave-the-activity teardown. Mirrors [onCleared]: marks
+     * the VM closed and routes both the speaker handle close (which
+     * releases the AudioRecord and clears the system mic indicator) and
+     * the listener close to [cleanupScope] so the teardown survives
+     * Activity destruction. Call this from the leave-the-room button
+     * BEFORE finishing the activity; relying on [onCleared] alone leaves
+     * a window where the AudioRecord stays held while the activity is
+     * paused / queued for destruction.
+     */
+    fun leave() {
+        if (closed) return
+        closed = true
+        requestedSpeakers = emptySet()
+        teardownBroadcast(BroadcastUiState.Idle, finalCleanup = true)
+        teardown(targetState = ConnectionUiState.Closed, finalCleanup = true)
+    }
+
     override fun onCleared() {
         closed = true
         teardownBroadcast(BroadcastUiState.Idle, finalCleanup = true)