Add realtime transcript notification in v2 (#15344)

- emit a typed `thread/realtime/transcriptUpdated` notification from
live realtime transcript deltas
- expose that notification as flat `threadId`, `role`, and `text` fields
instead of a nested transcript array
- continue forwarding raw `handoff_request` items on
`thread/realtime/itemAdded`, including the accumulated
`active_transcript`
- update app-server docs, tests, and generated protocol schema artifacts
to match the delta-based payloads

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/tui_app_server/src/app/app_server_adapter.rs

@@ -482,6 +482,9 @@ fn server_notification_thread_target(
         ServerNotification::ThreadRealtimeItemAdded(notification) => {
             Some(notification.thread_id.as_str())
         }
+        ServerNotification::ThreadRealtimeTranscriptUpdated(notification) => {
+            Some(notification.thread_id.as_str())
+        }
         ServerNotification::ThreadRealtimeOutputAudioDelta(notification) => {
             Some(notification.thread_id.as_str())
         }

codex-rs/tui_app_server/src/chatwidget.rs

@@ -6069,6 +6069,7 @@ impl ChatWidget {
             | ServerNotification::ContextCompacted(_)
             | ServerNotification::FuzzyFileSearchSessionUpdated(_)
             | ServerNotification::FuzzyFileSearchSessionCompleted(_)
+            | ServerNotification::ThreadRealtimeTranscriptUpdated(_)
             | ServerNotification::WindowsWorldWritableWarning(_)
             | ServerNotification::WindowsSandboxSetupCompleted(_)
             | ServerNotification::AccountLoginCompleted(_) => {}