feat: add service name to app-server (#12319)

Add service name to the app-server so that the app can use it's own
service name

This is on thread level because later we might plan the app-server to
become a singleton on the computer

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -13323,6 +13323,12 @@
                 "type": "null"
               }
             ]
+          },
+          "serviceName": {
+            "type": [
+              "string",
+              "null"
+            ]
           }
         },
         "title": "ThreadStartParams",