[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/client_tests.rs

@@ -89,6 +89,7 @@ fn sample_turn_start_request() -> ClientRequest {
         request_id: RequestId::Integer(1),
         params: TurnStartParams {
             thread_id: "thread-1".to_string(),
+            client_user_message_id: None,
             input: Vec::new(),
             ..Default::default()
         },
@@ -101,6 +102,7 @@ fn sample_turn_steer_request() -> ClientRequest {
         params: TurnSteerParams {
             thread_id: "thread-1".to_string(),
             expected_turn_id: "turn-1".to_string(),
+            client_user_message_id: None,
             input: Vec::new(),
             responsesapi_client_metadata: None,
             additional_context: None,