Add Phase B: Inventory COGS auto-posting to GL on JobUsage transactions

When powder is consumed via a job (JobsController) or scan (InventoryController.LogUsage),
debit the item's CogsAccountId and credit its InventoryAccountId for the cost of the
quantity consumed (using AverageCost if available, else UnitCost). No-op when either
GL account is not configured on the InventoryItem.

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

src/PowderCoating.Web/Controllers/InventoryController.cs

@@ -30,6 +30,7 @@ public class InventoryController : Controller
     private readonly IInventoryAiLookupService _aiLookupService;
     private readonly ISubscriptionService _subscriptionService;
     private readonly UserManager<ApplicationUser> _userManager;
+    private readonly IAccountBalanceService _accountBalanceService;
 
     public InventoryController(
         IUnitOfWork unitOfWork,
@@ -39,7 +40,8 @@ public class InventoryController : Controller
         IMeasurementConversionService measurementService,
         IInventoryAiLookupService aiLookupService,
         ISubscriptionService subscriptionService,
-        UserManager<ApplicationUser> userManager)
+        UserManager<ApplicationUser> userManager,
+        IAccountBalanceService accountBalanceService)
     {
         _unitOfWork = unitOfWork;
         _mapper = mapper;
@@ -49,6 +51,7 @@ public class InventoryController : Controller
         _aiLookupService = aiLookupService;
         _subscriptionService = subscriptionService;
         _userManager = userManager;
+        _accountBalanceService = accountBalanceService;
     }
 
     /// <summary>
@@ -1552,6 +1555,14 @@ public class InventoryController : Controller
             await _unitOfWork.InventoryTransactions.AddAsync(txn);
             await _unitOfWork.SaveChangesAsync();
 
+            // GL: DR COGS, CR Inventory Asset — no-op if accounts not configured on the item
+            if (item.CogsAccountId.HasValue && item.InventoryAccountId.HasValue)
+            {
+                var cost = quantity * (item.AverageCost > 0 ? item.AverageCost : item.UnitCost);
+                await _accountBalanceService.DebitAsync(item.CogsAccountId, cost);
+                await _accountBalanceService.CreditAsync(item.InventoryAccountId, cost);
+            }
+
             // PowderUsageLog requires a specific JobItem + Coat FK — scan-based logging
             // doesn't have that context, so we rely on the InventoryTransaction alone
             // for the audit trail. Coat-level PowderUsageLogs are created by the job workflow.