1. User form: add hint that email is used as login username
2. Dashboard low stock widget: only show products below min_stock_level (was showing all)
3. Dashboard attendance widget: link to filtered view showing only sessions without attendance
4. Trainer form: require at least one activity selected (validation + UI)
5. Cross-reference: show activities on trainer list, show trainers on activity cards
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>