Support the ent26 enterprise plan (#35238)

## What changed

- Recognize `ent26` in authentication, account protocol, backend rate-limit
  payloads, and generated app-server schemas.
- Treat it as an enterprise workspace plan for cloud-config eligibility and
  business-style usage-limit guidance.
- Cover token parsing, serialization, backend mapping, plan classification,
  cloud-config access, and usage-limit formatting with tests.

GitOrigin-RevId: 537d897c8b1d80bcdb66d0fd402563fbb8c5a277

codex-rs/login/src/token_data_tests.rs

@@ -69,6 +69,21 @@ fn id_token_info_parses_hc_plan_as_enterprise() {
     assert_eq!(info.is_workspace_account(), true);
 }
 
+#[test]
+fn id_token_info_parses_ent26_plan() {
+    let fake_jwt = fake_jwt(serde_json::json!({
+        "email": "user@example.com",
+        "https://api.openai.com/auth": {
+            "chatgpt_plan_type": "ent26"
+        }
+    }));
+
+    let info = parse_chatgpt_jwt_claims(&fake_jwt).expect("should parse");
+    assert_eq!(info.get_chatgpt_plan_type().as_deref(), Some("Enterprise"));
+    assert_eq!(info.get_chatgpt_plan_type_raw().as_deref(), Some("ent26"));
+    assert_eq!(info.is_workspace_account(), true);
+}
+
 #[test]
 fn id_token_info_parses_usage_based_business_plans() {
     let self_serve_business_jwt = fake_jwt(serde_json::json!({