Add pagination/search/sort to the admin tables that can grow large

Uses simple-datatables (vanilla JS, no jQuery needed) on the Users,
Sessions, Email Log, and Feedback tables, since those grow with real
usage. Left Games (small, admin-curated) and Hints (row order is
meaningful - "checked in order" - a sortable column would mislead)
untouched.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

assets/app.js

@@ -8,3 +8,4 @@ import 'bootstrap/js/dist/dropdown';
 import './game-waiting';
 import './game-lobby';
 import './admin-session-tabs';
+import './admin-datatables';