Adds RegionalTargetResponse, RegionalBudgetResponse,
RegionAgencyMapResponse, RegionalTaxRuleResponse,
RegionHierarchyResponse, and RegionDashboardResponse types, plus
setTarget/setBudget/mapAgency/setTaxRule/hierarchy/dashboard methods
on the regions API client, mirroring the new backend endpoints.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Introduced FlatPaymentController under Distribution.Features.Payment, providing GET and POST endpoints at /api/payments. Supports listing, retrieving, and creating payments with filtering and error handling. Business logic is delegated to PaymentService.