Extended /platform/cron/index.php with billing invoice auto-generation (getDueBillingSubscriptions, generateInvoice, processAutoPayment per site). Built Platform Admin Billing UI at /platform/administration/financials/?page=billing with 4 pages: Dashboard (MRR/ARR/revenue by plan/past due/upcoming renewals), Plan Management (CRUD with modal form), Invoice Management (DataTable with filter/generate/void), Overage Rates (inline rate editing). Fixed email_quota_usage column names (sent_count, period_date). End-to-end test: Site 8 invoice INV-2026-03-0002 generated with 17 line items totaling .84.