fix(ui): fallback to permissions when permissions.fields is undefined for group fields (#17812)

[Rodrigoue9]

Title

fix(ui): fallback to parent permissions when field permissions are undefined for group fields (#17812)

Description

• Updates GroupFieldComponent to pass (permissions?.fields ?? permissions) to RenderFields for named group fields.
• Fixes bug where group children were dropped during render because top-level collections or globals with default permissions did not define an explicit permissions.fields sub-object.
• Ensures all child inputs inside group fields render properly in the admin panel.

Closes #17812