- _list_tables now accepts a user param and delegates to
get_accessible_tables: admins see all, non-admins see only tables
covered by their resource_grants. Fixes silent leak of table names
to unauthorised analysts.
- today derived from now.date() (UTC) instead of date.today()
(server-local TZ), so today and now are always consistent.
- Updated test_render_override_tables_list to seed an admin user so
RBAC filtering doesn't hide the table; added three new tests covering
per-user table isolation, admin sees-all, and no-grants-empty.