fix: skip LLM call for group messages without @bot

Only forward group chat messages to OpenClaw LLM when the bot is
@-mentioned. Non-@ messages are still saved to history but no longer
consume API calls or tokens.

src/process.py

@@ -385,6 +385,13 @@ class OpenClawBridge(BasePlugin):
             return "ok"
 
         # ===== 所有用户正常对话（整合后的统一流程）=====
+        # 群聊消息没有@机器人时，不调LLM
+        if self.ctx.group is not None:
+            at_me = f"[CQ:at,qq={self.ctx.rebot_id}]" in self.ctx.raw_message
+            if not at_me:
+                logger.info(f"Group chat without @bot from {sender_id}, skipped LLM call")
+                return
+
         session_key = self._build_session_key()
         context_msg = self._build_context_with_history(raw_message, identity_tag)
         reply = self._send_to_openclaw(context_msg, session_key)