Add config bundle transport types (#24617)

## Summary

PR 1 of 5 in the cloud-managed config client stack.

Adds the generated backend models and client transport surface for the
config bundle endpoint. This bundle endpoint is the replacement backend
surface for legacy cloud requirements; the final PR in the stack
switches runtime consumers over to it.

## Details

- This is transport-only plumbing: no runtime config behavior changes in
this PR.
- The bundle endpoint is the new shared backend surface for
cloud-delivered config and requirements data.
- Both supported path styles are wired here: `/api/codex/config/bundle`
and `/wham/config/bundle`.
- The response types come from generated backend models so later PRs
consume the backend contract directly instead of maintaining
hand-written mirror structs.

## Validation

Validated through the targeted stack checks after rebasing onto current
`main`:

- Rust crate tests for
config/hooks/cloud-config/backend-client/app-server-protocol
- Filtered `codex-core` and `codex-app-server` `cloud_config_bundle`
tests
- Python generated-file contract test
- `cargo shear --deny-warnings`
- Targeted `argument-comment-lint` for config/hooks

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

@@ -6,7 +6,11 @@ pub use client::Client;
 pub use client::RequestError;
 pub use types::CodeTaskDetailsResponse;
 pub use types::CodeTaskDetailsResponseExt;
+pub use types::ConfigBundleResponse;
 pub use types::ConfigFileResponse;
+pub use types::DeliveredConfigToml;
+pub use types::DeliveredRequirementsToml;
+pub use types::DeliveredTomlFragment;
 pub use types::PaginatedListTaskListItem;
 pub use types::TaskListItem;
 pub use types::TurnAttemptsSiblingTurnsResponse;