Support model-owned token budget defaults (#35608)

## What changed

- Add token-budget settings to model catalog messages and apply them when the
  feature is enabled without explicit token-budget configuration.
- Keep explicit user settings authoritative, reject invalid catalog defaults,
  and preserve resolved defaults in exported config locks.
- Manage context-window guidance through world state so it updates once when
  the active model changes while retaining prior conversation history.

## Testing

- Cover catalog defaults, explicit overrides, disabled features, invalid
  values, config-lock replay, and model switching.

GitOrigin-RevId: 54544fefaa14b09f5ef5bad9967a13c52b87b0fe

codex-rs/core/src/session/turn_context.rs

@@ -536,6 +536,7 @@ impl Session {
         );
 
         let mut per_turn_config = per_turn_config;
+        super::token_budget::apply_model_defaults(&mut per_turn_config, &model_info);
         per_turn_config.service_tier = get_service_tier(
             per_turn_config.service_tier,
             per_turn_config.features.enabled(Feature::FastMode),