Expose multi-agent versions in model/list (#37433)

## What changed

- Add nullable `multiAgentVersion` metadata to v2 `model/list` responses.
- Represent supported values as `disabled`, `v1`, or `v2` in the Rust API and generated JSON Schema and TypeScript exports.
- Forward the value from model catalog presets through app-server responses.

## Testing

- Extend the remote model catalog test fixture with a `v2` multi-agent version.

GitOrigin-RevId: bd3b2bbe0a3b562b4d1f03df7da2a73a35713978

codex-rs/app-server/src/models.rs

@@ -46,6 +46,7 @@ fn model_from_preset(preset: ModelPreset) -> Model {
         default_reasoning_effort: preset.default_reasoning_effort,
         input_modalities: preset.input_modalities,
         supports_personality: preset.supports_personality,
+        multi_agent_version: preset.multi_agent_version.map(Into::into),
         additional_speed_tiers: preset.additional_speed_tiers,
         service_tiers: preset
             .service_tiers