Add 4 dashboard/financial features: compact renewals, retroactive wizard fix, club revenue, expense shortcuts

- Compact overdue renewals alert into summary card with toggle detail list
- Rewrite retroactive enrollment wizard to CREATE new participants (not search existing)
- Add external revenue import form for club lump-sum payments
- Add quick-action buttons to financial overview for expenses/revenue
- Migration adds external_revenue to expenses category CHECK constraint
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>