Phase F: Customer/Vendor Statements, Payment Terms Parser, Tax Rates

F1: GetCustomerStatementAsync/GetVendorStatementAsync on IFinancialReportService;
    StatementLineDto; CustomerStatementDto/VendorStatementDto; Statement action on
    CustomersController + VendorsController; Statement views + PDF download via
    StatementPdfHelper (QuestPDF); Statement button on Customer/Vendor Details pages.

F2: PaymentTermsParser static helper (CalculateDueDate, ParseEarlyPaymentDiscount);
    EarlyPaymentDiscountPercent/Days on Invoice entity; GetCustomerPaymentTerms AJAX
    endpoint on InvoicesController auto-populates Terms + due date on customer select;
    early payment discount notice on Invoice Create.

F3: TaxRate entity (Name/Rate/State/IsDefault/IsActive, tenant-filtered);
    IUnitOfWork.TaxRates + UnitOfWork + ApplicationDbContext; TaxRatesController
    (Index/Create/Edit/Delete/ToggleActive, CompanyAdminOnly); GetTaxRateForCustomer
    AJAX endpoint; Tax Rates in Settings gear menu.

Also fixes AddVendorCredits migration: VendorCreditApplications FKs changed from
CASCADE to NoAction to resolve SQL Server error 1785 (multiple cascade paths).
Migration: AddPaymentTermsAndTaxRates applied locally; 200/200 unit tests pass.

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

src/PowderCoating.Infrastructure/Repositories/UnitOfWork.cs

@@ -154,6 +154,9 @@ public class UnitOfWork : IUnitOfWork
     // Bank Reconciliation
     private IRepository<BankReconciliation>? _bankReconciliations;
 
+    // Tax Rates
+    private IRepository<TaxRate>? _taxRates;
+
     /// <summary>
     /// Initialises the unit of work with the scoped <paramref name="context"/>.
     /// The context is shared across all repositories created by this instance so that
@@ -552,6 +555,11 @@ public class UnitOfWork : IUnitOfWork
     public IRepository<BankReconciliation> BankReconciliations =>
         _bankReconciliations ??= new Repository<BankReconciliation>(_context);
 
+    // Tax Rates
+    /// <summary>Repository for <see cref="TaxRate"/> named tax rates used to pre-fill invoice tax percent by jurisdiction.</summary>
+    public IRepository<TaxRate> TaxRates =>
+        _taxRates ??= new Repository<TaxRate>(_context);
+
     /// <summary>
     /// Flushes all pending changes in the EF Core change tracker to the database.
     /// Returns the number of state entries written.