refactor: restructure to core/ + ui/ with multi-threaded backend

core/client.py

@@ -0,0 +1,27 @@
+import threading
+from typing import Any, Dict
+
+from .server import BackendServer
+
+
+class BackendClient:
+    def __init__(self, server: BackendServer):
+        self._server = server
+        self._request_counter = 0
+        self._lock = threading.Lock()
+
+    def process_message(self, user_input: str, timeout: float = 30.0) -> Dict[str, Any]:
+        with self._lock:
+            self._request_counter += 1
+        return self._server.process_message(user_input, timeout)
+
+    def execute_tool(self, tool_name: str, arguments: Dict[str, Any], timeout: float = 10.0) -> str:
+        with self._lock:
+            self._request_counter += 1
+        return self._server.execute_tool(tool_name, arguments, timeout)
+
+    def update_config(self, api_key: str, base_url: str = "https://api.deepseek.com") -> None:
+        self._server.update_config(api_key, base_url)
+
+    def shutdown(self) -> None:
+        self._server.shutdown()