The custom Checkbox used Lucide Square/SquareCheck for unchecked/checked
states but had no indeterminateIcon, so MUI fell back to its default 24px
Material icon. This caused a visible size mismatch and row height jitter
in the bulk-select header of monitor tables.
Add SquareMinus from lucide-react at the same size (16px) and strokeWidth
(1.5) as the existing icons, and extend the checked color rule to also
cover the indeterminate state.