Gate realtime audio interruption logic to v2 (#14984)

- thread the realtime version into conversation start and app-server
notifications
- keep playback-aware mic gating and playback interruption behavior on
v2 only, leaving v1 on the legacy path

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

@@ -68,6 +68,7 @@ use codex_protocol::protocol::RateLimitSnapshot as CoreRateLimitSnapshot;
 use codex_protocol::protocol::RateLimitWindow as CoreRateLimitWindow;
 use codex_protocol::protocol::ReadOnlyAccess as CoreReadOnlyAccess;
 use codex_protocol::protocol::RealtimeAudioFrame as CoreRealtimeAudioFrame;
+use codex_protocol::protocol::RealtimeConversationVersion;
 use codex_protocol::protocol::ReviewDecision as CoreReviewDecision;
 use codex_protocol::protocol::SessionSource as CoreSessionSource;
 use codex_protocol::protocol::SkillDependencies as CoreSkillDependencies;
@@ -3708,6 +3709,7 @@ pub struct ThreadRealtimeStopResponse {}
 pub struct ThreadRealtimeStartedNotification {
     pub thread_id: String,
     pub session_id: Option<String>,
+    pub version: RealtimeConversationVersion,
 }
 
 /// EXPERIMENTAL - raw non-audio thread realtime item emitted by the backend.