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/backend-client/src/client.rs

@@ -706,6 +706,8 @@ impl Client {
             }
             crate::types::PlanType::Enterprise => AccountPlanType::Enterprise,
             crate::types::PlanType::Edu | crate::types::PlanType::Education => AccountPlanType::Edu,
+            crate::types::PlanType::EduPlus => AccountPlanType::EduPlus,
+            crate::types::PlanType::EduPro => AccountPlanType::EduPro,
             crate::types::PlanType::Guest
             | crate::types::PlanType::FreeWorkspace
             | crate::types::PlanType::Quorum