Credit AR for gift-certificate redemptions in balance recompute (audit O7)

ApplyGiftCertificate posts DR 2500 Gift Certificate Liability / CR AR, but the AR
recompute only subtracted payments and credit-memo applications — so the redemption's
2500 debit was recomputed while its AR credit was not, leaving the Trial Balance out
of balance by the total gift-certificate amount redeemed and overstating AR on the
Balance Sheet.

Subtract GC redemptions from AR in both recompute engines:
  - FinancialReportService: Balance Sheet (gcRedeemedBs) and Trial Balance (gcRedeemedTb)
  - LedgerService: AR section (dated rows) and ComputePriorBalanceAsync (prior balance)

AR Aging was already correct (uses BalanceDue, which includes GiftCertificateRedeemed).
Adds a LedgerService regression test. Build clean; 292 unit tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PowderCoating.Infrastructure/Services/LedgerService.cs

@@ -350,6 +350,27 @@ public class LedgerService : ILedgerService
                     LinkId = cm.InvoiceId
                 });
 
+            // Gift-certificate redemptions reduce open AR (CREDIT) — ApplyGiftCertificate posts DR 2500 / CR AR.
+            var arGcRedemptions = await _context.GiftCertificateRedemptions
+                .Include(r => r.Invoice)
+                .Include(r => r.GiftCertificate)
+                .Where(r => !r.IsDeleted && r.RedeemedDate >= fromDate && r.RedeemedDate <= toDate
+                         && r.Invoice.Status != InvoiceStatus.Voided)
+                .ToListAsync();
+
+            foreach (var r in arGcRedemptions)
+                entries.Add(new LedgerEntryDto
+                {
+                    Date = r.RedeemedDate,
+                    Reference = r.GiftCertificate?.CertificateCode ?? $"GC-{r.GiftCertificateId}",
+                    Source = "Gift Certificate",
+                    Description = $"GC redeemed on {r.Invoice?.InvoiceNumber}",
+                    Debit = 0,
+                    Credit = r.AmountRedeemed,
+                    LinkController = "Invoices",
+                    LinkId = r.InvoiceId
+                });
+
             // NOTE: cash refunds no longer touch AR. Under the "reverse the sale" model they debit
             // Sales Returns + Sales Tax Payable and credit the bank (see section 5b above).
         }
@@ -751,6 +772,11 @@ public class LedgerService : ILedgerService
                 .Where(a => a.AppliedDate < beforeDate && a.Invoice.Status != InvoiceStatus.Voided)
                 .SumAsync(a => (decimal?)a.AmountApplied) ?? 0;
 
+            // Gift-certificate redemptions credit AR (DR 2500 / CR AR), same as in GetAccountLedgerAsync.
+            credits += await _context.GiftCertificateRedemptions
+                .Where(r => !r.IsDeleted && r.RedeemedDate < beforeDate && r.Invoice.Status != InvoiceStatus.Voided)
+                .SumAsync(r => (decimal?)r.AmountRedeemed) ?? 0;
+
             // NOTE: cash refunds no longer debit AR — they reverse the sale (Sales Returns + Sales Tax),
             // handled in section 5b above.
         }