### What?
- Fixed an issue where virtual relationship fields (`virtual: string`,
e.g. `post.title`) could not be used in the WhereBuilder filter
dropdown.
- Ensured regular virtual fields (`virtual: true`) are still excluded
since they are not backed by database fields.
### Why?
Previously, attempting to filter by a virtual relationship caused
runtime errors because the field was treated as a plain text field. At
the same time, non-queryable virtuals needed to remain excluded to avoid
invalid queries.
### How?
- Updated `reduceFieldsToOptions` to recognize `virtual: string` fields
and map them to their underlying path while keeping their declared type
and operators.
- Continued to filter out `virtual: true` fields in the same guard used
for hidden/disabled fields.
7e98fbf78e
