Fix incoming powder inventory: defer creation to approval, deduplicate, fix category

Three bugs fixed:

1. Wrong timing — inventory items with IsIncoming=true were auto-created during
   quote save (in QuotePricingAssemblyService). Now deferred to quote approval so
   inventory only reflects powders the shop is actually going to process.

2. Duplicate records — same powder on multiple items in one quote created multiple
   inventory records. Now grouped by PowderCatalogItemId: one record per unique
   catalog powder, all matching coats linked to the same record.

3. Wrong category — category resolution used first IsCoating=true by DisplayOrder,
   which could land items in Cerakote or other unintended categories. Now prefers
   CategoryCode==POWDER explicitly, with DisplayOrder fallback.

Changes:
- QuoteItemCoat: add PowderCatalogItemId int? — persists catalog reference at quote
  save time so the approval path knows what to create
- QuotePricingAssemblyService.BuildQuoteItemCoatsAsync: store PowderCatalogItemId
  on coat instead of calling CreateIncomingInventoryItemAsync immediately
- QuotePricingAssemblyService.CreateIncomingInventoryItemAsync: signature changed
  from (coatDto, companyId) to (catalogItemId, companyId); category lookup prefers
  POWDER code; no longer clears PowderCostPerLb on the DTO
- QuotePricingAssemblyService.EnsureIncomingInventoryForApprovedQuoteAsync: new
  public method called at approval — loads pending coats, groups by catalog ID,
  creates one inventory item per group, links all coats in each group
- IQuotePricingAssemblyService: exposes EnsureIncomingInventoryForApprovedQuoteAsync
- QuotesController.ApproveQuote: calls EnsureIncomingInventory after save
- QuotesController.ChangeQuoteStatus: calls EnsureIncomingInventory on Approved
- QuoteApprovalController: injects IQuotePricingAssemblyService; calls
  EnsureIncomingInventory in ApproveInternal (customer-facing portal path)
- InventoryController.CreateIncomingFromCatalog: same category fix (prefers POWDER)
- Migration: AddPowderCatalogItemIdToCoat (nullable int on QuoteItemCoats)
- Tests: updated AddAsIncoming test to verify deferred behavior; new deduplication test

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

src/PowderCoating.Web/Controllers/QuotesController.cs

@@ -2317,6 +2317,17 @@ public class QuotesController : Controller
 
             _logger.LogInformation("Quote {QuoteId} approved by user {UserId}", id, currentUser.Id);
 
+            // Create incoming inventory records for any catalog-sourced coats that were deferred
+            // from quote-save time. One record per unique powder catalog item, de-duplicated.
+            try
+            {
+                await _quotePricingAssemblyService.EnsureIncomingInventoryForApprovedQuoteAsync(id, quote.CompanyId);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "EnsureIncomingInventory failed for quote {QuoteId} — continuing", id);
+            }
+
             // Notify customer that quote is approved (only if user opted in)
             if (sendEmail)
             {
@@ -2802,6 +2813,20 @@ public class QuotesController : Controller
             await _unitOfWork.Quotes.UpdateAsync(quote);
             await _unitOfWork.SaveChangesAsync();
 
+            // When transitioning to Approved: create incoming inventory records for catalog-sourced
+            // coats that were deferred from quote-save time (one record per unique powder, deduplicated).
+            if (newStatus.StatusCode == AppConstants.StatusCodes.Quote.Approved && oldStatusCode != AppConstants.StatusCodes.Quote.Approved)
+            {
+                try
+                {
+                    await _quotePricingAssemblyService.EnsureIncomingInventoryForApprovedQuoteAsync(request.QuoteId, quote.CompanyId);
+                }
+                catch (Exception ex)
+                {
+                    _logger.LogWarning(ex, "EnsureIncomingInventory failed for quote {QuoteId} — continuing", request.QuoteId);
+                }
+            }
+
             // Auto-create job when quote is approved — guard against double-conversion
             // (race condition: two simultaneous approval calls could both pass the oldStatusCode check)
             if (newStatus.StatusCode == AppConstants.StatusCodes.Quote.Approved && oldStatusCode != AppConstants.StatusCodes.Quote.Approved