fix: update TTS voice mapping to only use valid Edge TTS voices

Previously the voice map referenced 10+ non-existent Edge TTS voice names
(xiaohan, xiaochen, xiaoshuang, etc.), causing NoAudioReceived errors and
fallback to browser default TTS. Now only maps to the 6 actually available
Chinese voices (xiaoxiao, xiaoyi, yunxi, yunyang, yunjian, yunxia).
Added voice speed adjustments and fixed --rate argument format for Windows.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

android/app/src/main/java/com/tiangong/aiagent/ui/chat/ChatViewModel.kt

@@ -15,6 +15,7 @@ import com.tiangong.aiagent.domain.model.Message
 import com.tiangong.aiagent.domain.model.SseEvent
 import com.tiangong.aiagent.util.AudioPlayer
 import com.tiangong.aiagent.util.AudioRecorder
+import com.tiangong.aiagent.util.MarkdownRenderer
 import com.tiangong.aiagent.util.OfflineQueueManager
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.Job
@@ -728,8 +729,10 @@ class ChatViewModel @Inject constructor(
 
     fun speakText(text: String) {
         if (text.isBlank()) return
+        val plainText = MarkdownRenderer.stripMarkdownForTTS(text)
+        if (plainText.isBlank()) return
         viewModelScope.launch {
-            chatRepository.synthesizeSpeech(text)
+            chatRepository.synthesizeSpeech(plainText)
                 .onSuccess { audioUrl -> audioPlayer.play(audioUrl) }
                 .onFailure { Log.w("ChatViewModel", "TTS failed", it) }
         }

android/app/src/main/java/com/tiangong/aiagent/util/MarkdownRenderer.kt

@@ -28,6 +28,29 @@ import io.noties.markwon.linkify.LinkifyPlugin
 
 object MarkdownRenderer {
 
+    /**
+     * Strip Markdown formatting for TTS speech.
+     * Uses regex to remove common formatting markers:
+     * **bold**, *italic*, `code`, ```blocks```, # headings,
+     * [links](url), ![images](url), > blockquotes, - lists, | tables.
+     */
+    fun stripMarkdownForTTS(text: String): String {
+        if (text.isBlank()) return ""
+        return text
+            .replace(Regex("```[\\s\\S]*?```"), "")          // fenced code blocks
+            .replace(Regex("`([^`]*)`"), "$1")                // inline code
+            .replace(Regex("!\\[.*?]\\(.*?\\)"), "")           // images
+            .replace(Regex("\\[([^]]*)]\\(.*?\\)"), "$1")      // links -> text
+            .replace(Regex("(?m)^#{1,6}\\s+"), "")             // heading markers
+            .replace(Regex("(\\*{1,3}|_{1,3})(.*?)\\1"), "$2") // bold/italic
+            .replace(Regex("(?m)^[*-]\\s+"), "")               // list bullets
+            .replace(Regex("(?m)^>\\s*"), "")                  // blockquote
+            .replace(Regex("(?m)^---+$"), "")                  // horizontal rules
+            .replace("|", " ")                                 // table pipes
+            .replace(Regex("\\n{3,}"), "\n\n")                 // collapse excessive newlines
+            .trim()
+    }
+
     private var markwonInstance: Markwon? = null
 
     private fun getMarkwon(context: Context): Markwon {