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/codex-api/src/endpoint/realtime_websocket/methods_common.rs

@@ -8,6 +8,7 @@ use crate::endpoint::realtime_websocket::methods_v2::session_update_session as v
 use crate::endpoint::realtime_websocket::methods_v2::websocket_intent as v2_websocket_intent;
 use crate::endpoint::realtime_websocket::protocol::RealtimeEventParser;
 use crate::endpoint::realtime_websocket::protocol::RealtimeOutboundMessage;
+use crate::endpoint::realtime_websocket::protocol::RealtimeOutputModality;
 use crate::endpoint::realtime_websocket::protocol::RealtimeSessionConfig;
 use crate::endpoint::realtime_websocket::protocol::RealtimeSessionMode;
 use crate::endpoint::realtime_websocket::protocol::RealtimeVoice;
@@ -57,13 +58,14 @@ pub(super) fn session_update_session(
     event_parser: RealtimeEventParser,
     instructions: String,
     session_mode: RealtimeSessionMode,
+    output_modality: RealtimeOutputModality,
     voice: RealtimeVoice,
 ) -> SessionUpdateSession {
     let session_mode = normalized_session_mode(event_parser, session_mode);
     match event_parser {
         RealtimeEventParser::V1 => v1_session_update_session(instructions, voice),
         RealtimeEventParser::RealtimeV2 => {
-            v2_session_update_session(instructions, session_mode, voice)
+            v2_session_update_session(instructions, session_mode, output_modality, voice)
         }
     }
 }
@@ -73,6 +75,7 @@ pub fn session_update_session_json(config: RealtimeSessionConfig) -> JsonResult<
         config.event_parser,
         config.instructions,
         config.session_mode,
+        config.output_modality,
         config.voice,
     );
     session.id = config.session_id;