The padding around an enum filter's checkbox/radio carried the hover cue but
swallowed the click: the only element that toggles a Mantine Checkbox is its
native <label>, which wraps its own text and nothing else. The row's padding
and the gutter beside the input square lie outside it, so styling those on
`root` produced an area that looked interactive and was not.
Stretch a `::before` over the relatively-positioned root. The pseudo-element
belongs to the label's own box, so a click anywhere in the row lands on the
label and toggles the input. `cursor: pointer` moves to the root for the same
reason -- the affordance should cover exactly what is clickable.