Recompute inventory-consumption COGS and fix written-off AR (audit O6, O8)

O6: inventory consumed on jobs posts DR COGS / CR Inventory, but neither recompute
engine reflected it — so reports understated COGS / overstated inventory and a
"Recalculate Balances" wiped the effect. The COGS posting fires only for JobUsage
and Waste transaction types, which are created only at the two COGS-posting sites,
so the consumption is exactly identifiable from InventoryTransaction:
  - both posting sites now record consumption at the effective (weighted-average)
    unit cost so TotalCost equals the COGS posted (the recompute reads TotalCost)
  - LedgerService: new section (dated rows + prior balance) crediting Inventory /
    debiting COGS from JobUsage/Waste rows on items with both accounts mapped
  - FinancialReportService: Trial Balance + accrual P&L include consumption COGS
This reads existing transactions, so historical data is covered with no backfill.
The Balance Sheet inventory line is intentionally left alone — it does not track
inventory purchases either (periodic), so relieving it for consumption alone would
unbalance it; tracked as O9 (inventory capitalization policy).

O8: the write-off already creates a balanced posted JournalEntry (both engines read
it via their JE-line sections). The real defect was 4 "Status != WrittenOff" filters
in FinancialReportService that excluded pre-write-off payments from AR credits and
bank debits — leaving the paid portion dangling as open AR and understating the bank.
Removed those filters; AR now nets to zero for written-off invoices and the trial
balance balances. No backfill needed.

Adds a LedgerService regression test for inventory consumption. Build clean; 293
unit tests pass.

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

tests/PowderCoating.UnitTests/LedgerServiceTests.cs

@@ -655,6 +655,43 @@ public class LedgerServiceTests
         Assert.Equal(150m, ledger.ClosingBalance); // debit-normal AR: 200 invoiced − 50 redeemed
     }
 
+    // ── Inventory consumption posts DR COGS / CR Inventory; both sides must be in the ──
+    // ── recompute so a recalc reproduces them and the trial balance stays balanced (O6). ──
+
+    [Fact]
+    public async Task GetAccountLedgerAsync_InventoryConsumption_DebitsCogsAndCreditsInventory()
+    {
+        await using var context = CreateContext();
+        // COGS account (id 1) and Inventory asset account (id 2)
+        context.Accounts.Add(new Account { Id = 1, CompanyId = 1, AccountNumber = "5100", Name = "Powder & Materials", AccountType = AccountType.CostOfGoods, AccountSubType = AccountSubType.CostOfGoodsSold, IsActive = true });
+        context.Accounts.Add(new Account { Id = 2, CompanyId = 1, AccountNumber = "1200", Name = "Inventory - Powder", AccountType = AccountType.Asset, AccountSubType = AccountSubType.Inventory, IsActive = true });
+        context.InventoryItems.Add(new InventoryItem
+        {
+            Id = 7, CompanyId = 1, Name = "White Powder", SKU = "WP-1",
+            CogsAccountId = 1, InventoryAccountId = 2
+        });
+        context.InventoryTransactions.Add(new InventoryTransaction
+        {
+            Id = 1, CompanyId = 1, InventoryItemId = 7,
+            TransactionType = InventoryTransactionType.JobUsage,
+            Quantity = -4m, UnitCost = 10m, TotalCost = 40m,
+            TransactionDate = InPeriod, Reference = "Job 100"
+        });
+        await context.SaveChangesAsync();
+
+        var svc = CreateService(context);
+
+        var cogs = await svc.GetAccountLedgerAsync(1, PeriodStart, PeriodEnd);
+        var cogsEntry = Assert.Single(cogs!.Entries, e => e.Source == "Inventory Usage");
+        Assert.Equal(40m, cogsEntry.Debit);
+        Assert.Equal(40m, cogs.ClosingBalance); // debit-normal COGS
+
+        var inv = await svc.GetAccountLedgerAsync(2, PeriodStart, PeriodEnd);
+        var invEntry = Assert.Single(inv!.Entries, e => e.Source == "Inventory Usage");
+        Assert.Equal(40m, invEntry.Credit);
+        Assert.Equal(-40m, inv.ClosingBalance); // debit-normal asset relieved by a credit
+    }
+
     private static LedgerService CreateService(ApplicationDbContext context)
         => new LedgerService(context, Mock.Of<ILogger<LedgerService>>());