fix(app-server): for external auth, replace id_token with chatgpt_acc… (#11240)

…ount_id and chatgpt_plan_type

### Summary
Following up on external auth mode which was introduced here:
https://github.com/openai/codex/pull/10012

Turns out some clients have a differently shaped ID token and don't have
a chosen workspace (aka chatgpt_account_id) encoded in their ID token.
So, let's replace `id_token` param with `chatgpt_account_id` and
`chatgpt_plan_type` (optional) when initializing the external ChatGPT
auth mode (`account/login/start` with `chatgptAuthTokens`).

The client was able to test end-to-end with a Codex build from this
branch and verified it worked!

codex-rs/app-server-protocol/schema/json/ChatgptAuthTokensRefreshResponse.json

@@ -4,13 +4,19 @@
     "accessToken": {
       "type": "string"
     },
-    "idToken": {
+    "chatgptAccountId": {
       "type": "string"
+    },
+    "chatgptPlanType": {
+      "type": [
+        "string",
+        "null"
+      ]
     }
   },
   "required": [
     "accessToken",
-    "idToken"
+    "chatgptAccountId"
   ],
   "title": "ChatgptAuthTokensRefreshResponse",
   "type": "object"