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/Data/ApplicationDbContext.cs

@@ -332,6 +332,9 @@ public class ApplicationDbContext : IdentityDbContext<ApplicationUser>, IDataPro
     /// <summary>Bank reconciliation sessions matching GL transactions to bank statements; tenant-filtered with soft delete.</summary>
     public DbSet<BankReconciliation> BankReconciliations { get; set; }
 
+    /// <summary>Named tax rates used to pre-fill invoice tax percent by jurisdiction; tenant-filtered with soft delete.</summary>
+    public DbSet<TaxRate> TaxRates { get; set; }
+
     /// <summary>Credit notes received from vendors (returned goods, pricing disputes); tenant-filtered with soft delete.</summary>
     public DbSet<VendorCredit> VendorCredits { get; set; }
     /// <summary>Expense-reversal line items on a vendor credit; soft-delete only.</summary>
@@ -638,12 +641,29 @@ public class ApplicationDbContext : IdentityDbContext<ApplicationUser>, IDataPro
         modelBuilder.Entity<BankReconciliation>().HasQueryFilter(e =>
             !e.IsDeleted && (IsPlatformAdmin || e.CompanyId == CurrentCompanyId));
 
+        // Tax Rates: tenant-filtered
+        modelBuilder.Entity<TaxRate>().HasQueryFilter(e =>
+            !e.IsDeleted && (IsPlatformAdmin || e.CompanyId == CurrentCompanyId));
+
         // Vendor Credits: tenant-filtered; child rows soft-delete only
         modelBuilder.Entity<VendorCredit>().HasQueryFilter(e =>
             !e.IsDeleted && (IsPlatformAdmin || e.CompanyId == CurrentCompanyId));
         modelBuilder.Entity<VendorCreditLineItem>().HasQueryFilter(e => !e.IsDeleted);
         modelBuilder.Entity<VendorCreditApplication>().HasQueryFilter(e => !e.IsDeleted);
 
+        // VendorCreditApplication: NoAction on both FKs to avoid SQL Server multiple-cascade-path error 1785.
+        // Bills and VendorCredits both cascade-delete through Vendor, creating two paths to VendorCreditApplications.
+        modelBuilder.Entity<VendorCreditApplication>()
+            .HasOne(vca => vca.Bill)
+            .WithMany()
+            .HasForeignKey(vca => vca.BillId)
+            .OnDelete(DeleteBehavior.NoAction);
+        modelBuilder.Entity<VendorCreditApplication>()
+            .HasOne(vca => vca.VendorCredit)
+            .WithMany()
+            .HasForeignKey(vca => vca.VendorCreditId)
+            .OnDelete(DeleteBehavior.NoAction);
+
         // Purchase Orders
         modelBuilder.Entity<PurchaseOrder>().HasQueryFilter(e =>
             !e.IsDeleted && (IsPlatformAdmin || e.CompanyId == CurrentCompanyId));