[codex] Forward turn moderation metadata through app-server (#25710)

## Why
First-party backends can supply turn-scoped moderation metadata that
app-server clients need for client-side presentation. Exposing this as
an experimental typed notification lets opted-in clients consume it
without interpreting raw Responses API events.

## What changed
- forward `response.metadata.openai_chatgpt_moderation_metadata` from
Responses API SSE and WebSocket streams as turn-scoped moderation
metadata
- emit the experimental app-server v2 `turn/moderationMetadata`
notification with `{ threadId, turnId, metadata }`
- add app-server integration coverage for the typed moderation metadata
notification

## Testing
- `just test -p codex-core
build_ws_client_metadata_includes_window_lineage_and_turn_metadata`
- `just test -p codex-core` (fails locally: 46 failures and 1 timeout,
primarily missing `test_stdio_server` and shell snapshot timeouts)
- `just test -p codex-app-server-protocol`
- `just test -p codex-app-server
turn_moderation_metadata_emits_typed_notification_v2`
- `just test -p codex-app-server` (fails locally: 792 passed, 10 failed,
and 5 timed out; failures are in existing environment-sensitive tests,
primarily because nested macOS `sandbox-exec` is not permitted)
- `just write-app-server-schema --experimental --schema-root
/tmp/codex-app-server-schema-experimental`

codex-rs/app-server/src/outgoing_message.rs

@@ -725,6 +725,7 @@ mod tests {
     use codex_app_server_protocol::RateLimitWindow;
     use codex_app_server_protocol::ServerResponse;
     use codex_app_server_protocol::ToolRequestUserInputParams;
+    use codex_app_server_protocol::TurnModerationMetadataNotification;
     use codex_protocol::ThreadId;
     use pretty_assertions::assert_eq;
     use serde_json::json;
@@ -951,6 +952,31 @@ mod tests {
         );
     }
 
+    #[test]
+    fn verify_turn_moderation_metadata_notification_serialization() {
+        let notification =
+            ServerNotification::TurnModerationMetadata(TurnModerationMetadataNotification {
+                thread_id: "thread-1".to_string(),
+                turn_id: "turn-1".to_string(),
+                metadata: json!({"presentation": "inline"}),
+            });
+
+        let jsonrpc_notification = OutgoingMessage::AppServerNotification(notification);
+        assert_eq!(
+            json!({
+                "method": "turn/moderationMetadata",
+                "params": {
+                    "threadId": "thread-1",
+                    "turnId": "turn-1",
+                    "metadata": {"presentation": "inline"},
+                },
+            }),
+            serde_json::to_value(jsonrpc_notification)
+                .expect("ensure the notification serializes correctly"),
+            "ensure the notification serializes correctly"
+        );
+    }
+
     #[test]
     fn server_request_response_from_result_decodes_typed_response() {
         let request = ServerRequest::CommandExecutionRequestApproval {