Add realtime output modality and transcript events (#17701)

- Add outputModality to thread/realtime/start and wire text/audio output
selection through app-server, core, API, and TUI.\n- Rename the realtime
transcript delta notification and add a separate transcript done
notification that forwards final text from item done without correlating
it with deltas.

codex-rs/core/tests/suite/compact_remote.rs

@@ -17,6 +17,7 @@ use codex_protocol::protocol::ItemStartedEvent;
 use codex_protocol::protocol::Op;
 use codex_protocol::protocol::RealtimeConversationRealtimeEvent;
 use codex_protocol::protocol::RealtimeEvent;
+use codex_protocol::protocol::RealtimeOutputModality;
 use codex_protocol::protocol::RolloutItem;
 use codex_protocol::protocol::RolloutLine;
 use codex_protocol::user_input::UserInput;
@@ -116,6 +117,7 @@ async fn start_remote_realtime_server() -> responses::WebSocketTestServer {
 async fn start_realtime_conversation(codex: &codex_core::CodexThread) -> Result<()> {
     codex
         .submit(Op::RealtimeConversationStart(ConversationStartParams {
+            output_modality: RealtimeOutputModality::Audio,
             prompt: Some(Some("backend prompt".to_string())),
             session_id: None,
             transport: None,