[codex-rs] auto-review model override (#23767)

## Why

Guardian auto-review normally uses the provider-preferred review model
when one is available. Some parent models need model-catalog metadata to
select a different review model while keeping older `/models` payloads
compatible when that metadata is absent.

## What changed

- Added optional `ModelInfo::auto_review_model_override` metadata to the
public model payload as a review-model slug.
- Updated Guardian review model selection to prefer the catalog override
when present, while preserving the existing provider preferred-model
path and parent-model fallback when it is omitted.
- Added focused Guardian coverage for override and no-override model
selection.
- Added an `auto_review` core integration suite test that loads override
metadata from a remote model catalog path and asserts the strict
auto-review `/responses` request uses the catalog-selected review model.
- Updated existing `ModelInfo` fixtures and local catalog constructors
for the new optional field.

## Validation

- `cargo test -p codex-protocol
model_info_defaults_availability_nux_to_none_when_omitted`
- `cargo test -p codex-core guardian_review_uses_`
- `cargo test -p codex-core
remote_model_override_uses_catalog_model_for_strict_auto_review --test
all`
- `just fix -p codex-protocol`
- `just fix -p codex-core`
- `just fmt`
- `git diff --check`

codex-rs/codex-api/tests/models_integration.rs

@@ -98,6 +98,7 @@ async fn models_client_hits_models_endpoint() {
             input_modalities: default_input_modalities(),
             used_fallback_model_metadata: false,
             supports_search_tool: false,
+            auto_review_model_override: None,
             tool_mode: None,
         }],
     };