voice: play/pause toggle, stop previous on new track

- ViewModel: _currentPlayingPath tracks active track. Tap same → stop.
  Tap different → stop old, play new. onComplete clears currentPlayingPath.
- AudioRecorderManager: stopPlayback() already called at start (existing)
- VoiceBubble: simplified click, always sends to ViewModel for state management

tools/chatgui-android/app/src/main/java/com/utun/chat/ui/components/MessageBubble.kt

@@ -107,11 +107,9 @@ private fun VoiceBubble(message: Message, textColor: Color, onPlay: (String, ()
             Box(
                 modifier = Modifier.size(32.dp).background(Color.White, CircleShape)
                     .clickable {
-                        if (!playing && message.filePath.isNotEmpty()) {
+                        if (message.filePath.isNotEmpty()) {
                             playing = true; elapsedMs = 0; progress = 0f
                             onPlay(message.filePath, onDone)
-                        } else {
-                            playing = false; onDone()
                         }
                     },
                 contentAlignment = Alignment.Center

tools/chatgui-android/app/src/main/java/com/utun/chat/viewmodel/ChatViewModel.kt

@@ -264,9 +264,22 @@ class ChatViewModel : ViewModel() {
         NativeLib.voiceSetCompressorConfig(maxGainDb, lookbackMs, lookaheadMs, riseRate, targetLevelDb)
     }
 
+    private var _currentPlayingPath: String? = null
+
     fun playVoiceMessage(filePath: String, onComplete: () -> Unit) {
+        if (_currentPlayingPath == filePath) {
+            audioRecorder.stopPlayback()
+            _currentPlayingPath = null
+            onComplete()
+            return
+        }
+        audioRecorder.stopPlayback()
+        _currentPlayingPath = filePath
         LogManager.addLog("INFO", "VM", "play voice: $filePath")
-        audioRecorder.playVoiceFile(filePath, onComplete = onComplete)
+        audioRecorder.playVoiceFile(filePath, onComplete = {
+            _currentPlayingPath = null
+            onComplete()
+        })
     }
 
     fun clearState() {