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.Core/Entities/Accounting.cs

@@ -285,3 +285,20 @@ public class VendorCreditApplication : BaseEntity
     public virtual VendorCredit VendorCredit { get; set; } = null!;
     public virtual Bill Bill { get; set; } = null!;
 }
+
+/// <summary>
+/// A named tax rate (e.g., "CA Sales Tax 8.25%") used to pre-fill the TaxPercent field on
+/// invoices when a taxable customer is selected. Companies can define multiple rates for
+/// different jurisdictions and mark one as default.
+/// </summary>
+public class TaxRate : BaseEntity
+{
+    public string Name { get; set; } = string.Empty;
+    /// <summary>Rate as a percentage, e.g., 8.25 means 8.25%.</summary>
+    public decimal Rate { get; set; }
+    public string? State { get; set; }
+    public string? Description { get; set; }
+    /// <summary>When true, this rate is auto-applied to new invoices for taxable customers.</summary>
+    public bool IsDefault { get; set; }
+    public bool IsActive { get; set; } = true;
+}

src/PowderCoating.Core/Entities/Invoice.cs

@@ -42,6 +42,19 @@ public class Invoice : BaseEntity
     public string? Terms { get; set; }
     public string? CustomerPO { get; set; }
 
+    /// <summary>
+    /// Early payment discount percentage (e.g., 2 means 2% discount).
+    /// Parsed from the customer's payment terms when the invoice is created (e.g., "2/10 Net 30").
+    /// Informational only — does not automatically reduce the amount due.
+    /// </summary>
+    public decimal EarlyPaymentDiscountPercent { get; set; }
+
+    /// <summary>
+    /// Number of days after invoice date within which the early payment discount applies.
+    /// Parsed from the customer's payment terms (e.g., "2/10 Net 30" → 10 days).
+    /// </summary>
+    public int EarlyPaymentDiscountDays { get; set; }
+
     /// <summary>
     /// Original invoice number from an external system (e.g. QuickBooks invoice # "3048").
     /// Stored for searchability and traceability after import. Searchable from the invoice list.