Add Pro Max plan support and update Pro display names (#47971)

## What changed

- Recognize `promax` in authentication, account responses, and backend rate limits; update generated schemas and client types.
- Display `prolite` as “Pro”, `pro` as “Pro (More)”, and `promax` as “Pro (Max)” in account labels, status, and analytics.
- Include Pro Max in experimental context eligibility, paid-plan tooltips, and usage-limit guidance for purchasing credits.

## Testing

Extend coverage for Pro Max plan parsing, account and rate-limit responses, experimental context eligibility, and plan display names. Update the login token test to expect “Pro (More)”.

GitOrigin-RevId: 197e00fa7a99cbce125c8f1d43a451ec1ed5c1fb

codex-rs/backend-client/src/client.rs

@@ -781,6 +781,7 @@ impl Client {
             crate::types::PlanType::Plus => AccountPlanType::Plus,
             crate::types::PlanType::Pro => AccountPlanType::Pro,
             crate::types::PlanType::ProLite => AccountPlanType::ProLite,
+            crate::types::PlanType::ProMax => AccountPlanType::ProMax,
             crate::types::PlanType::Team => AccountPlanType::Team,
             crate::types::PlanType::SelfServeBusinessProLite => {
                 AccountPlanType::SelfServeBusinessProLite