Add tests for nested promoted widget resolution paths in safeWidgetMapper

## Context

This issue tracks the need to add dedicated test coverage for the new nested resolution paths in `safeWidgetMapper` introduced in PR #9282.

## Test Coverage Needed

The following fields in `SafeWidgetData` need test coverage for promoted widgets whose concrete source is two layers deep:
- `storeNodeId`
- `storeName`
- `effectiveWidget` type resolution

## Scenario

A promoted widget whose concrete source is nested two layers deep should produce the correct `storeNodeId`, `storeName`, and `type` in `SafeWidgetData`.

## References

- Pull Request: https://github.com/Comfy-Org/ComfyUI_frontend/pull/9282
- Original Discussion: https://github.com/Comfy-Org/ComfyUI_frontend/pull/9282#discussion_r2866949168
- Requested by: @christian-byrne

## File

`src/composables/graph/useGraphNodeManager.ts`

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-9292-Add-tests-for-nested-promoted-widget-resolution-paths-in-safeWidgetMapper-3156d73d3650814184b1c82edfbf09c0) by [Unito](https://www.unito.io)