-- Each admin can pick their own theme for the backend (admin panel) only,
-- independent of the site-wide frontend theme (settings.theme, admin/design.php)
-- shown to real visitors. NULL means no personal preference set -- falls
-- back to 'default' in src/Settings.php's resolution, not the frontend
-- theme, since the two are deliberately decoupled.

ALTER TABLE admin_users ADD COLUMN theme VARCHAR(16) NULL AFTER role;
