fix(wecom): update connection status after WebSocket reconnection

The WeCom adapter's _listen_loop() automatically reconnects when the
WebSocket drops, but it never called _mark_connected() after a successful
reconnection. This left the runtime status file (gateway_state.json) stuck
in "disconnected" even though the adapter was fully operational again.

Add self._mark_connected() right after _open_connection() succeeds so
that the dashboard and health probes report the correct state.

Tested by forcing a WebSocket close via the heartbeat loop and verifying
that the status file updated from "disconnected" back to "connected".

gateway/platforms/wecom.py

@@ -345,6 +345,7 @@ class WeComAdapter(BasePlatformAdapter):
                 try:
                     await self._open_connection()
                     backoff_idx = 0
+                    self._mark_connected()
                     logger.info("[%s] Reconnected", self.name)
                 except Exception as reconnect_exc:
                     logger.warning("[%s] Reconnect failed: %s", self.name, reconnect_exc)