Add Phase A accounting features: AP Aging, Trial Balance, Cash vs Accrual

- AP Aging report (GetApAgingAsync, controller actions, view, PDF export)
  mirrors AR Aging — groups open bills by vendor, buckets by days past due date
- Trial Balance report (GetTrialBalanceAsync, view, PDF export)
  uses Account.CurrentBalance, groups by AccountType, validates debits == credits
- Cash vs Accrual accounting method setting on Company entity
  switchable at any time — report-time only, no GL re-posting on change
  P&L cash: revenue = payments received; expenses = bills/expenses paid in period
  Balance Sheet cash: omits AR and AP lines (no receivables/payables concept)
  AccountingMethod badge shown on P&L and Balance Sheet views
- Migration A (AddAccountingMethod) applied, default = Accrual for all existing companies
- AP Aging and Trial Balance added to Reports Landing page

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

src/PowderCoating.Application/DTOs/Accounting/FinancialReportDtos.cs

@@ -2,6 +2,72 @@ using PowderCoating.Core.Enums;
 
 namespace PowderCoating.Application.DTOs.Accounting;
 
+// Accounting method badge — set on report DTOs so views can show "Cash Basis" / "Accrual Basis"
+// without needing a separate round-trip to the company settings.
+
+
+// ── AP Aging ──────────────────────────────────────────────────────────────────
+
+public class ApAgingReportDto
+{
+    public DateTime AsOf { get; set; }
+    public string CompanyName { get; set; } = string.Empty;
+
+    public List<ApAgingVendorDto> Vendors { get; set; } = new();
+
+    public decimal TotalCurrent { get; set; }
+    public decimal Total1to30   { get; set; }
+    public decimal Total31to60  { get; set; }
+    public decimal Total61to90  { get; set; }
+    public decimal TotalOver90  { get; set; }
+    public decimal TotalOutstanding => TotalCurrent + Total1to30 + Total31to60 + Total61to90 + TotalOver90;
+}
+
+public class ApAgingVendorDto
+{
+    public int VendorId { get; set; }
+    public string VendorName { get; set; } = string.Empty;
+    public List<ApAgingBillDto> Bills { get; set; } = new();
+    public decimal TotalCurrent { get; set; }
+    public decimal Total1to30   { get; set; }
+    public decimal Total31to60  { get; set; }
+    public decimal Total61to90  { get; set; }
+    public decimal TotalOver90  { get; set; }
+    public decimal TotalBalance => TotalCurrent + Total1to30 + Total31to60 + Total61to90 + TotalOver90;
+}
+
+public class ApAgingBillDto
+{
+    public int BillId { get; set; }
+    public string BillNumber { get; set; } = string.Empty;
+    public DateTime BillDate { get; set; }
+    public DateTime? DueDate  { get; set; }
+    public decimal BalanceDue { get; set; }
+    public int DaysOverdue    { get; set; }
+}
+
+// ── Trial Balance ─────────────────────────────────────────────────────────────
+
+public class TrialBalanceDto
+{
+    public DateTime AsOf { get; set; }
+    public string CompanyName { get; set; } = string.Empty;
+    public List<TrialBalanceLine> Lines { get; set; } = new();
+    public decimal TotalDebits  { get; set; }
+    public decimal TotalCredits { get; set; }
+    public bool IsBalanced => Math.Abs(TotalDebits - TotalCredits) < 0.01m;
+}
+
+public class TrialBalanceLine
+{
+    public int AccountId           { get; set; }
+    public string AccountNumber    { get; set; } = string.Empty;
+    public string AccountName      { get; set; } = string.Empty;
+    public AccountType AccountType { get; set; }
+    public decimal DebitBalance    { get; set; }
+    public decimal CreditBalance   { get; set; }
+}
+
 // ── Profit & Loss ─────────────────────────────────────────────────────────────
 
 public class ProfitAndLossDto
@@ -9,6 +75,7 @@ public class ProfitAndLossDto
     public DateTime From { get; set; }
     public DateTime To { get; set; }
     public string CompanyName { get; set; } = string.Empty;
+    public AccountingMethod AccountingMethod { get; set; } = AccountingMethod.Accrual;
 
     public List<FinancialReportLine> RevenueLines { get; set; } = new();
     public decimal TotalRevenue { get; set; }
@@ -40,6 +107,7 @@ public class BalanceSheetDto
 {
     public DateTime AsOf { get; set; }
     public string CompanyName { get; set; } = string.Empty;
+    public AccountingMethod AccountingMethod { get; set; } = AccountingMethod.Accrual;
 
     // Assets
     public List<FinancialReportLine> CurrentAssets { get; set; } = new();