Suppress debug logs for model routing and ignore empty tools arrays

- Comment out verbose routing logs in the API server to reduce noise.
- Remove the `tools` field from Qwen client requests when it is an empty array.
- Add guards in Claude, Codex, Gemini‑CLI, and Gemini translators to skip tool conversion when the `tools` array is empty, preventing unnecessary payload modifications.

internal/client/qwen_client.go

@@ -329,6 +329,11 @@ func (c *QwenClient) APIRequest(ctx context.Context, modelName, endpoint string,
 		}
 	}
 
+	toolsResult := gjson.GetBytes(jsonBody, "tools")
+	if toolsResult.IsArray() && len(toolsResult.Array()) == 0 {
+		jsonBody, _ = sjson.DeleteBytes(jsonBody, "tools")
+	}
+
 	streamResult := gjson.GetBytes(jsonBody, "stream")
 	if streamResult.Exists() && streamResult.Type == gjson.True {
 		jsonBody, _ = sjson.SetBytes(jsonBody, "stream_options.include_usage", true)