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/Interfaces/IFinancialReportService.cs

@@ -1,4 +1,5 @@
 using PowderCoating.Application.DTOs.Accounting;
+using PowderCoating.Core.Enums;
 
 namespace PowderCoating.Application.Interfaces;
 
@@ -6,14 +7,16 @@ namespace PowderCoating.Application.Interfaces;
 /// Read-only service for financial aggregate reports. All methods query the database
 /// with AsNoTracking and return pre-shaped DTOs — no tracked entities are returned.
 /// Implemented in Infrastructure; uses ApplicationDbContext directly.
+/// The <paramref name="method"/> parameter overrides the company's stored preference when
+/// supplied; pass <c>null</c> to fall back to the company's configured accounting method.
 /// </summary>
 public interface IFinancialReportService
 {
     /// <summary>Returns a Profit &amp; Loss report for the given company and date range.</summary>
-    Task<ProfitAndLossDto> GetProfitAndLossAsync(int companyId, DateTime from, DateTime to);
+    Task<ProfitAndLossDto> GetProfitAndLossAsync(int companyId, DateTime from, DateTime to, AccountingMethod? method = null);
 
     /// <summary>Returns a Balance Sheet snapshot as of the given date.</summary>
-    Task<BalanceSheetDto> GetBalanceSheetAsync(int companyId, DateTime asOf);
+    Task<BalanceSheetDto> GetBalanceSheetAsync(int companyId, DateTime asOf, AccountingMethod? method = null);
 
     /// <summary>Returns an AR Aging report bucketed at 0-30, 31-60, 61-90, and 90+ days.</summary>
     Task<ArAgingReportDto> GetArAgingAsync(int companyId, DateTime asOf);
@@ -23,4 +26,13 @@ public interface IFinancialReportService
 
     /// <summary>Returns an invoice-basis Sales Tax Liability report for the given company and date range.</summary>
     Task<SalesTaxReportDto> GetSalesTaxReportAsync(int companyId, DateTime from, DateTime to);
+
+    /// <summary>Returns an AP Aging report bucketed at 0-30, 31-60, 61-90, and 90+ days past the bill due date.</summary>
+    Task<ApAgingReportDto> GetApAgingAsync(int companyId, DateTime asOf);
+
+    /// <summary>Returns a Trial Balance using current account balances as of the given date.</summary>
+    Task<TrialBalanceDto> GetTrialBalanceAsync(int companyId, DateTime asOf);
+
+    /// <summary>Looks up the accounting method configured for the given company. Returns Accrual if not found.</summary>
+    Task<AccountingMethod> GetCompanyAccountingMethodAsync(int companyId);
 }