Fix UI missing protocol version header causing agents endpoint 400

The ProtocolVersionInterceptor requires X-Cameleer-Protocol-Version: 1
on /api/v1/agents/** but the UI client middleware wasn't sending it,
causing the agents GET to fail silently in the command palette.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/api/client.ts

@@ -19,6 +19,7 @@ const authMiddleware: Middleware = {
     if (token) {
       request.headers.set('Authorization', `Bearer ${token}`);
     }
+    request.headers.set('X-Cameleer-Protocol-Version', '1');
     return request;
   },
   async onResponse({ response }) {