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/schema/json/ServerNotification.json

@@ -1694,6 +1694,13 @@
       ],
       "type": "object"
     },
+    "RealtimeConversationVersion": {
+      "enum": [
+        "v1",
+        "v2"
+      ],
+      "type": "string"
+    },
     "ReasoningEffort": {
       "description": "See https://platform.openai.com/docs/guides/reasoning?api-mode=responses#get-started-with-reasoning",
       "enum": [
@@ -2857,10 +2864,14 @@
         },
         "threadId": {
           "type": "string"
+        },
+        "version": {
+          "$ref": "#/definitions/RealtimeConversationVersion"
         }
       },
       "required": [
-        "threadId"
+        "threadId",
+        "version"
       ],
       "type": "object"
     },