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.Web/Views/Vendors/Details.cshtml

@@ -10,6 +10,9 @@
 <div class="row justify-content-center">
     <div class="col-lg-10">
         <div class="d-flex justify-content-end gap-2 mb-4">
+            <a asp-action="Statement" asp-route-id="@Model.Id" class="btn btn-outline-secondary">
+                <i class="bi bi-journal-text me-2"></i>Statement
+            </a>
             <a asp-action="Edit" asp-route-id="@Model.Id" class="btn btn-warning">
                 <i class="bi bi-pencil me-2"></i>Edit
             </a>