feat: add data tables demo powered by Tabulator

Adds tables/data.html with a jQuery-free data table backed by
Tabulator 6 (MIT, currently the most actively maintained option in the
DataTables-alternative space).

Features wired up:

- Sorting (column header click)
- Header filters per column (text input on name / email, list filter
  on role / status)
- Status badges via a custom cell formatter
- Global filter input in the card header
- Pagination with page-size selector
- Movable columns (drag column headers to reorder)
- CSV and JSON download buttons
- Print button
- Bootstrap 5 theme (tabulator_bootstrap5.min.css) so the table matches
  the rest of the dashboard out of the box

Tabulator loads from jsDelivr; nothing is bundled into adminlte.js.
Sidenav entry lands in a later commit.