feat(park): 子应用 lifespan 接入 s2s 实时语音栈（S2S_ENABLED=1 时后台起 :8765）

导入 .s2s_bridge.start_s2s_backend 并以 stop 事件控制；依赖 speech_to_speech
（vendor/s2s-cloud），启用前需 uv pip install -e app/park/vendor/s2s-cloud。

app/park/app.py

@@ -33,6 +33,15 @@ async def lifespan(app: FastAPI):
 
     stop = threading.Event()
 
+    # s2s 实时语音栈（可选）：后台线程起 RealtimeServer(:8765)，仅 S2S_ENABLED=1
+    # 依赖 speech_to_speech（vendor/s2s-cloud，需先 `uv pip install -e app/park/vendor/s2s-cloud`）
+    if settings.S2S_ENABLED:
+        try:
+            from .s2s_bridge import start_s2s_backend
+            start_s2s_backend(stop)
+        except Exception as e:  # noqa: BLE001
+            log.warning("s2s 语音栈启动失败（S2S_ENABLED=1 但依赖未装?）: %s", e)
+
     def tick_loop():
         while not stop.is_set():
             try: