[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/state/src/extract.rs

@@ -200,6 +200,7 @@ mod tests {
     fn event_msg_user_messages_set_title_and_first_user_message() {
         let mut metadata = metadata_for_test();
         let item = RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: format!("{USER_MESSAGE_BEGIN} actual user request"),
             images: Some(vec![]),
             local_images: vec![],
@@ -221,6 +222,7 @@ mod tests {
     fn event_msg_image_only_user_message_sets_image_placeholder_preview() {
         let mut metadata = metadata_for_test();
         let item = RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: String::new(),
             images: Some(vec!["https://example.com/image.png".to_string()]),
             local_images: vec![],
@@ -245,6 +247,7 @@ mod tests {
     fn event_msg_blank_user_message_without_images_keeps_first_user_message_empty() {
         let mut metadata = metadata_for_test();
         let item = RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: "   ".to_string(),
             images: Some(vec![]),
             local_images: vec![],
@@ -285,6 +288,7 @@ mod tests {
         assert_eq!(metadata.title, "");
 
         let user_item = RolloutItem::EventMsg(EventMsg::UserMessage(UserMessageEvent {
+            client_id: None,
             message: format!("{USER_MESSAGE_BEGIN} next normal prompt"),
             images: Some(vec![]),
             local_images: vec![],