fix(msggateway): reset read deadline in pong handler to prevent Web client timeout

Root cause:
Due to browser API restrictions, Web (Wasm) clients cannot actively send standard WebSocket Ping frames. They rely entirely on server-initiated Pings (every 27s) and automatic browser Pong responses to maintain the connection. The `pongHandler` was empty and failed to reset the connection's read deadline upon receiving a Pong, causing the server's read loop to strictly time out at 30 seconds.

Solution:
Call `c.setReadDeadline()` inside the `pongHandler` to properly extend the connection's lifespan when a Pong frame is received.

internal/msggateway/client_conn.go

@@ -208,7 +208,11 @@ func (c *websocketClientConn) pingHandler(appData string) error {
 	return nil
 }
 
-func (c *websocketClientConn) pongHandler(string) error {
+func (c *websocketClientConn) pongHandler(appData string) error {
+	log.ZDebug(context.Background(), "pong handler recv pong", "remoteAddr", c.conn.RemoteAddr(), "appData", appData)
+	if err := c.setReadDeadline(); err != nil {
+		return err
+	}
 	return nil
 }