feat: add runtime listen-only switch and API controls

qingjian_cs/app/runtime_switch.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+import threading
+
+
+_lock = threading.Lock()
+_listen_only_mode = False
+
+
+def set_listen_only(enabled: bool) -> bool:
+    global _listen_only_mode
+    with _lock:
+        _listen_only_mode = bool(enabled)
+        return _listen_only_mode
+
+
+def is_listen_only() -> bool:
+    with _lock:
+        return _listen_only_mode
+