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/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -15594,16 +15594,6 @@
           },
           {
             "properties": {
-              "internal_chat_message_metadata_passthrough": {
-                "anyOf": [
-                  {
-                    "$ref": "#/definitions/v2/InternalChatMessageMetadataPassthrough"
-                  },
-                  {
-                    "type": "null"
-                  }
-                ]
-              },
               "type": {
                 "enum": [
                   "compaction_trigger"