Support Edu Plus and Edu Pro account plans (#39316)

## What changed

- Recognize `edu_plus` and `edu_pro` as distinct education workspace plans across authentication, backend rate-limit mapping, and app-server account schemas.
- Include both plans in cloud configuration eligibility and use the education usage-limit behavior.
- Display the plans as `Edu Plus` and `Edu Pro` in the TUI status view.

## Testing

- Cover parsing, workspace classification, account and rate-limit responses, cloud configuration eligibility, usage-limit messages, and TUI display names for the new variants.

GitOrigin-RevId: bf8add780ae03a3c6d10c4f4afa0da262c37928e

codex-rs/codex-backend-openapi-models/src/models/rate_limit_status_payload.rs

@@ -134,6 +134,10 @@ pub enum PlanType {
     Enterprise,
     #[serde(rename = "edu")]
     Edu,
+    #[serde(rename = "edu_plus")]
+    EduPlus,
+    #[serde(rename = "edu_pro")]
+    EduPro,
     #[serde(rename = "unknown", other)]
     Unknown,
 }