Track client-authored developer messages in rollout history (#38243)

## What changed

- Mark developer messages received from clients with `client_authored` harness
  metadata when `retain_client_developer_messages` is enabled.
- Carry that provenance through pending input and persist it alongside rollout
  response items without adding it to provider requests or the serialized
  `TurnInput` payload.
- Preserve existing behavior for unannotated response items and when the
  feature is disabled.

## Testing

- Cover client item injection before and during turns, additional application
  context, rollout replay, image resize notices, and serialization boundaries.

GitOrigin-RevId: f385c177732becde732272e4b8440eb91f5c1039

codex-rs/rollout/src/tests.rs

@@ -1331,7 +1331,7 @@ async fn read_head_for_summary_omits_harness_metadata() {
         ordinal: None,
         item: RolloutItem::ResponseItem(ResponseItemEnvelope {
             item: response_item.clone(),
-            metadata: Some(CodexHarnessMetadata {}),
+            metadata: Some(CodexHarnessMetadata::default()),
         }),
     };
     fs::write(