fix(tts): gate auto reply by ENABLE_TTS; allow on-demand and manual playback

- Pipeline: skip _send_tts_audio only for non-manual when ENABLE_TTS=false;
  remove enable_tts early return from handle_tts_request_on_demand.
- Tencent TTS: PrimaryLanguage/chunking follow user language preference only.
- Expo: let manual tts_audio bypass late-segment playback gate after interrupt.
- Docs: clarify ENABLE_TTS vs tts_request in api/.env.example and TTSProvider port.
- Tests: add manual bypass cases; adjust pipeline language tests for en+Chinese text.

Co-authored-by: Cursor <cursoragent@cursor.com>

api/app/features/conversation/ws/pipeline.py

@@ -115,7 +115,8 @@ async def _send_tts_audio(
         settings.enable_tts,
         settings.tts_provider,
     )
-    if not settings.enable_tts:
+    # enable_tts：仅禁用「助手回复自动生成 TTS」（want_tts 路径）；用户点喇叭（manual=True）仍可合成。
+    if not manual and not settings.enable_tts:
         logger.info(
             "pipeline._send_tts_audio result conversation_id={} chunk_index={} ok=False "
             "url_set=False audio_bytes_len=0 reason=enable_tts_false",
@@ -269,14 +270,6 @@ async def handle_tts_request_on_demand(
         settings.enable_tts,
         settings.tts_provider,
     )
-    if not settings.enable_tts:
-        logger.info(
-            "pipeline.handle_tts_request_on_demand result ok=False reason=未开启语音合成 "
-            "conversation_id={} assistant_message_id={}",
-            conversation_id,
-            assistant_message_id,
-        )
-        return False, "未开启语音合成"
 
     conv = await db.get(Conversation, conversation_id)
     if not conv or conv.user_id != user_id or conv.deleted_at is not None: