Refresh on models etag mismatch (#8491)

- Send models etag
- Refresh models on 412
- This wires `ModelsManager` to `ModelFamily` so we don't mutate it
mid-turn

codex-rs/otel/src/otel_manager.rs

@@ -511,6 +511,7 @@ impl OtelManager {
                 "reasoning_summary_part_added".into()
             }
             ResponseEvent::RateLimits(_) => "rate_limits".into(),
+            ResponseEvent::ModelsEtag(_) => "models_etag".into(),
         }
     }