fix: stop/pause no longer fires onComplete from killed thread

When stopPlayback/pausePlayback kills the playback thread, the thread's
onComplete callback was still firing, resetting UI state (playing=false,
elapsed=0). Added @Volatile 'stopped' flag — onComplete only fires on
natural completion, not on external stop/pause.

tools/chatgui-android/app/src/main/java/com/utun/chat/data/AudioRecorderManager.kt

@@ -185,6 +185,7 @@ class AudioRecorderManager {
     @Volatile var elapsedMs: Int = 0; private set
     var pausedElapsedMs: Int = 0; private set
     private var playThread: Thread? = null
+    @Volatile private var stopped = false
 
     fun playVoiceFile(filePath: String, onProgress: ((Float) -> Unit)? = null, onComplete: () -> Unit = {}) {
         playFromPosition(filePath, 0, onProgress, onComplete)
@@ -245,19 +246,22 @@ class AudioRecorderManager {
             } catch (e: Exception) {
                 LogManager.addLog("ERROR", "AudioPlayer", "play error: ${e.message}")
             }
-            playing = false; isPaused = false
-            onComplete()
+            if (!stopped) {
+                playing = false; isPaused = false; onComplete()
+            }
         }.apply { start() }
     }
 
     fun pausePlayback() {
         pausedElapsedMs = elapsedMs
-        isPaused = true; playing = false
+        stopped = true; isPaused = true; playing = false
         playThread?.join(500); playThread = null
+        stopped = false
     }
 
     fun stopPlayback() {
-        playing = false; isPaused = false; pausedElapsedMs = 0
+        stopped = true; playing = false; isPaused = false; pausedElapsedMs = 0
         playThread?.join(500); playThread = null
+        stopped = false
     }
 }