feat: 大屏后端（FastAPI+MQTT+sim_engine）

- REST :10085 / MQTT 控制 / SSE 回退 / AI+语音
- 数据源规划：接核心服务端 + 算力引擎真实数据

backend/vendor/s2s-cloud/tests/test_llm_utils.py

@@ -0,0 +1,9 @@
+from speech_to_speech.LLM.utils import remove_unspeechable
+
+
+def test_remove_unspeechable_normalizes_smart_apostrophes() -> None:
+    assert remove_unspeechable("I’ll reply if here’s the plan.") == "I'll reply if here's the plan."
+
+
+def test_remove_unspeechable_keeps_text_and_drops_emoji() -> None:
+    assert remove_unspeechable("Hello 👋 lobster 🦞") == "Hello  lobster "