Feat: add upgrade to app server modelList (#10556)

### Summary
* Add model upgrade to listModel app server endpoint to support
dynamically show model upgrade banner.

codex-rs/app-server-protocol/schema/json/v2/ModelListResponse.json

@@ -59,6 +59,12 @@
         "supportsPersonality": {
           "default": false,
           "type": "boolean"
+        },
+        "upgrade": {
+          "type": [
+            "string",
+            "null"
+          ]
         }
       },
       "required": [