fix: resolve 5 invoice/payment issues from user feedback

- Replace misleading 'sent' status with 'pending' (no email capability)
- Show assessment group name instead of raw 'regular_assessment' type
- Add owner last name to invoice table
- Fix payment creation Internal Server Error (PostgreSQL $2 type cast)
- Add edit/delete capability for payment records with invoice recalc

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/database/tenant-schema.service.ts

@@ -157,7 +157,7 @@ export class TenantSchemaService {
         amount DECIMAL(10,2) NOT NULL,
         amount_paid DECIMAL(10,2) DEFAULT 0.00,
         status VARCHAR(20) DEFAULT 'draft' CHECK (status IN (
-          'draft', 'sent', 'paid', 'partial', 'overdue', 'void', 'written_off'
+          'draft', 'pending', 'sent', 'paid', 'partial', 'overdue', 'void', 'written_off'
         )),
         period_start DATE,
         period_end DATE,