[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/analytics/src/analytics_client_tests.rs

@@ -272,6 +272,7 @@ fn sample_turn_start_request(thread_id: &str, request_id: i64) -> ClientRequest
         request_id: RequestId::Integer(request_id),
         params: TurnStartParams {
             thread_id: thread_id.to_string(),
+            client_user_message_id: None,
             input: vec![
                 UserInput::Text {
                     text: "hello".to_string(),
@@ -391,6 +392,7 @@ fn sample_turn_steer_request(
         params: TurnSteerParams {
             thread_id: thread_id.to_string(),
             expected_turn_id: expected_turn_id.to_string(),
+            client_user_message_id: None,
             input: vec![
                 UserInput::Text {
                     text: "more".to_string(),