fix: change unknown source message log from error to debug level (#239)

* Initial plan

* Change console.error to console.debug for unknown message sources

Co-authored-by: liady <7003853+liady@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: liady <7003853+liady@users.noreply.github.com>

Author: Copilot

src/message-transport.ts

@@ -75,7 +75,7 @@ export class PostMessageTransport implements Transport {
   ) {
     this.messageListener = (event) => {
       if (eventSource && event.source !== this.eventSource) {
-        console.error("Ignoring message from unknown source", event);
+        console.debug("Ignoring message from unknown source", event);
         return;
       }
       const parsed = JSONRPCMessageSchema.safeParse(event.data);