Add Frameless Bidi support for realtime conversations (#33261)

## What changed

- Add realtime conversation version `v3`, which preserves the V1 Codex Voice behavior while using Frameless Bidi `delegation.*` events.
- Translate audio, transcripts, handoffs, session context, and lifecycle events between the app server and the Frameless Bidi wire protocol.
- Support `v3` over WebSocket and WebRTC, including the Frameless `/live` endpoint, session configuration, headers, and default model selection.
- Update the app-server protocol schemas and documentation for the new version.

## Testing

- Add unit coverage for Frameless event parsing, outbound messages, context chunking, URL construction, and call creation.
- Add app-server end-to-end coverage for WebSocket delegation and WebRTC session startup.

GitOrigin-RevId: 79a3307bc209e1a54582ebd2febc07c909fca016

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -3304,7 +3304,7 @@ mod tests {
                 prompt: Some(Some("You are on a call".to_string())),
                 realtime_session_id: Some("sess_456".to_string()),
                 transport: None,
-                version: Some(RealtimeConversationVersion::V1),
+                version: Some(RealtimeConversationVersion::V3),
                 voice: Some(RealtimeVoice::Marin),
             },
         };
@@ -3325,7 +3325,7 @@ mod tests {
                     "prompt": "You are on a call",
                     "realtimeSessionId": "sess_456",
                     "transport": null,
-                    "version": "v1",
+                    "version": "v3",
                     "voice": "marin"
                 }
             }),

codex-rs/app-server-protocol/src/protocol/v2/realtime.rs

@@ -80,9 +80,9 @@ pub struct ThreadRealtimeStartParams {
     /// Optional prefix added to automatic Codex response items when `codexResponsesAsItems` is true.
     #[ts(optional = nullable)]
     pub codex_response_item_prefix: Option<String>,
-    /// Optional prefix added to automatic V1 Codex commentary sent with
-    /// `conversation.handoff.append` when `codexResponsesAsItems` is not true. Final answers are
-    /// sent without the prefix.
+    /// Optional prefix added to automatic V1 or V3 Codex commentary sent through the selected
+    /// Bidi handoff wire event when `codexResponsesAsItems` is not true. Final answers are sent
+    /// without the prefix.
     #[ts(optional = nullable)]
     pub codex_response_handoff_prefix: Option<String>,
     /// Overrides the configured realtime model for this session only.