[codex] Add user input client ids (#24653)

## Summary

Adds an optional `clientId` field to app-server v2 `UserInput` and
carries it through the core `UserInput` model so clients can correlate
echoed user input items without relying on payload equality.

## Details

- Adds `client_id: Option<String>` to core `UserInput` variants.
- Exposes the v2 app-server field as `clientId` on the wire and in
generated TypeScript.
- Preserves the id when converting between app-server v2 and core
protocol types.
- Regenerates app-server schema fixtures.

## Validation

- `just fmt`
- `just write-app-server-schema`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-protocol`
- `just fix -p codex-app-server-protocol`
- `just fix -p codex-protocol`
- `git diff --check`

codex-rs/exec/src/lib.rs

@@ -779,6 +779,7 @@ async fn run_exec_session(args: ExecRunArgs) -> anyhow::Result<()> {
                     request_id: request_ids.next(),
                     params: TurnStartParams {
                         thread_id: primary_thread_id_for_span.clone(),
+                        client_user_message_id: None,
                         input: items.into_iter().map(Into::into).collect(),
                         responsesapi_client_metadata: None,
                         additional_context: None,