Attribute executor skill invocations to plugins (#39309)

## What changed

- Carry selected plugin identities from MCP discovery into per-turn extension data, limited to capability roots that are ready for the turn.
- Annotate executor skill catalog entries with the matching plugin ID and `user` scope.
- Include that attribution in `skill_invocation` analytics for both explicit and implicit executor skill invocations.

## Testing

- Extend the executor skills app-server test to verify plugin ID, skill scope, and invocation type for explicit and implicit analytics events.

GitOrigin-RevId: 9345600ae29bcb8eb894fffd2d6f7b05f22ebf74

codex-rs/ext/mcp/tests/executor_plugin_mcp.rs

@@ -134,6 +134,7 @@ async fn selected_plugin_package_is_contributed_without_servers_or_connectors()
             plugin_id,
             plugin_display_name,
             connector_ids,
+            ..
         } = contribution
         else {
             return None;