feat(app-server): expose rate-limit reset credits

AGENTS.md

@@ -261,6 +261,7 @@ These guidelines apply to app-server protocol work in `codex-rs`, especially:
   `*Params` for request payloads, `*Response` for responses, and `*Notification` for notifications.
 - Expose RPC methods as `<resource>/<method>` and keep `<resource>` singular (for example, `thread/read`, `app/list`).
 - Always expose fields as camelCase on the wire with `#[serde(rename_all = "camelCase")]` unless a tagged union or explicit compatibility requirement needs a targeted rename.
+- Always expose string enum values as camelCase on the wire with matching serde and TS `rename_all = "camelCase"` annotations unless an explicit compatibility requirement needs targeted renames.
 - Exception: config RPC payloads are expected to use snake_case to mirror config.toml keys (see the config read/write/list APIs in `app-server-protocol/src/protocol/v2.rs`).
 - Always set `#[ts(export_to = "v2/")]` on v2 request/response/notification types so generated TypeScript lands in the correct namespace.
 - Never use `#[serde(skip_serializing_if = "Option::is_none")]` for v2 API payload fields.