[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/core/src/codex_delegate_tests.rs

@@ -129,6 +129,7 @@ async fn forward_ops_preserves_submission_trace_context() {
     let submission = Submission {
         id: "sub-1".to_string(),
         op: Op::Interrupt,
+        client_user_message_id: None,
         trace: Some(codex_protocol::protocol::W3cTraceContext {
             traceparent: Some(
                 "00-1234567890abcdef1234567890abcdef-1234567890abcdef-01".to_string(),