[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/tui/src/chatwidget/tests/app_server.rs

@@ -283,6 +283,7 @@ async fn live_app_server_user_message_item_completed_does_not_duplicate_rendered
             completed_at_ms: 0,
             item: AppServerThreadItem::UserMessage {
                 id: "user-1".to_string(),
+                client_id: None,
                 content: vec![AppServerUserInput::Text {
                     text: "Hi, are you there?".to_string(),
                     text_elements: Vec::new(),

codex-rs/tui/src/chatwidget/tests/helpers.rs

@@ -722,6 +722,7 @@ pub(super) fn replay_user_message_inputs(
     chat.replay_thread_item(
         AppServerThreadItem::UserMessage {
             id: item_id.to_string(),
+            client_id: None,
             content,
         },
         "turn-1".to_string(),
@@ -946,6 +947,7 @@ pub(super) fn complete_user_message_for_inputs(
             completed_at_ms: 0,
             item: AppServerThreadItem::UserMessage {
                 id: item_id.to_string(),
+                client_id: None,
                 content,
             },
         }),

codex-rs/tui/src/chatwidget/tests/review_mode.rs

@@ -182,6 +182,7 @@ async fn live_app_server_review_prompt_item_is_not_rendered() {
             completed_at_ms: 0,
             item: AppServerThreadItem::UserMessage {
                 id: "review-prompt".to_string(),
+                client_id: None,
                 content: vec![AppServerUserInput::Text {
                     text: "Review the code changes against the base branch 'main'.".to_string(),
                     text_elements: Vec::new(),

codex-rs/tui/src/chatwidget/user_messages.rs

@@ -578,6 +578,7 @@ impl ChatWidget {
                 UserInput::Text {
                     text,
                     text_elements: current_text_elements,
+                    ..
                 } => append_text_with_rebased_elements(
                     &mut message,
                     &mut text_elements,