fix: return rotated refresh token from agent token refresh endpoint

Previously the refresh endpoint only returned a new accessToken, causing
agents to lose their refreshToken after the first refresh cycle and
forcing a full re-registration every ~2 hours.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/api/schema.d.ts

@@ -1069,9 +1069,10 @@ export interface components {
         AgentRefreshRequest: {
             refreshToken: string;
         };
-        /** @description Refreshed access token */
+        /** @description Refreshed access and refresh tokens */
         AgentRefreshResponse: {
             accessToken: string;
+            refreshToken: string;
         };
         /** @description Command to send to agent(s) */
         CommandRequest: {