feat(router): 在路由模式下仅处理特定命令

在路由模式下，本地仅处理路由相关命令（/nodes, /node, /help等），其他会话命令直接转发到节点。同时优化路由代理逻辑，对于会话命令直接转发到活跃节点，减少不必要的LLM调用。

bot/commands.py

@@ -67,6 +67,12 @@ async def handle_command(user_id: str, text: str) -> Optional[str]:
     cmd, args = parsed
     logger.info("Command: %s args=%r user=...%s", cmd, args[:50], user_id[-8:])
 
+    # In ROUTER_MODE, only handle router-specific commands locally.
+    # Session commands (/status, /new, /close, etc.) fall through to node forwarding.
+    from config import ROUTER_MODE
+    if ROUTER_MODE and cmd not in ("/nodes", "/node", "/help", "/h", "/?"):
+        return None
+
     set_current_user(user_id)
 
     if cmd in ("/new", "/n"):