- Contracts now store vat_percentage (1%), utilities_percentage, late_fee_type
  (none/daily/weekly/monthly), late_fee_rate, and grand_total
- New rental_invoices table with per-invoice breakdown: base, utilities, VAT,
  late_fee, total; late fee is calculated at payment time based on days overdue
- RentalInvoiceService handles generation, late-fee calc, and mark-paid
- Accounting auto-posts on rental.invoice_paid: Dr. Cash, Cr. RentalRevenue
  (410521) + ServiceRevenue (410515) + TaxPayable (230804) + FineRevenue (410512)
- contract_form has live preview calculator for monthly invoice totals
- contract_show shows full financial breakdown and invoices table
- Migrations: Phase_95_001 (alter contracts), Phase_95_002 (create invoices)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>