Add row selection to the contacts table so multiple contacts can be
deleted at once instead of one at a time.
- New Checkbox UI primitive wrapping @base-ui/react/checkbox, matching
the switch.tsx token conventions (incl. indeterminate state).
- Header select-all + per-row checkboxes; row-checkbox clicks stop
propagation so they don't open the detail sheet.
- Bulk action bar with selected count, Clear, and a role-gated
"Delete selected" action.
- handleBulkDelete via .delete().in('id', ids) — RLS already restricts
deletes to account members, so no migration/API route is needed.
- Selection is page-scoped and resets whenever the contact set reloads.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
