feat(core): store turn_id on ResponseItem metadata (#28360)

## Description

This PR is a followup to https://github.com/openai/codex/pull/28355 and
starts assigning `internal_chat_message_metadata_passthrough.turn_id` to
durable Responses API items created during a turn.

The goal is that those items keep the `turn_id` that introduced them
when Codex resends stateless HTTP context, reconstructs history for
resume/fork paths, or reuses websocket response state.

## What changed

- Set `internal_chat_message_metadata_passthrough.turn_id` when missing
as response items enter durable history, initial/replacement history,
inter-agent communication history, and local compaction summaries.
- Preserve existing item turn IDs instead of overwriting them during
persistence, resume reconstruction, compaction, forked history, and
websocket incremental reuse.
- Keep `compaction_trigger` fieldless because it is a request control,
not a durable response item.
- Update focused history/request assertions and fixtures for stateless
requests, websocket incrementals, compaction, thread injection, prompt
debug, and related CI coverage.

codex-rs/core/src/compact_remote_v2.rs

@@ -234,9 +234,7 @@ async fn run_remote_compact_task_inner_impl(
     )
     .await?;
     let mut input = prompt_input.clone();
-    input.push(ResponseItem::CompactionTrigger {
-        internal_chat_message_metadata_passthrough: None,
-    });
+    input.push(ResponseItem::CompactionTrigger {});
     let prompt = Prompt {
         input,
         tools: tool_router.model_visible_specs(),