Add IsIncoming inventory flag and catalog-to-incoming powder flow in item wizard

- InventoryItem.IsIncoming: marks powder ordered but not yet received; enables QR code
  printing on work orders while the shipment is in transit
- InventoryController.CreateIncomingFromCatalog: POST endpoint creates a 0-balance inventory
  record from a PowderCatalogItem and returns it in wizard-compatible shape
- item-wizard.js: custom coat tab now searches the platform powder catalog as a fallback;
  catalog results show an 'Add as Incoming Order' option; createIncomingFromCatalog POSTs
  to server and selects the new item without a page refresh
- QuoteItemCoatDto: CatalogItemId + AddAsIncoming fields so the wizard can signal server-side
  incoming-item creation during quote save
- Inventory Create/Edit/Index views: IsIncoming badge and field
- IInventoryAiLookupService: minor interface update
- Migration: AddInventoryIsIncoming

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

src/PowderCoating.Web/Views/Inventory/Edit.cshtml

@@ -398,6 +398,17 @@
                                 <textarea asp-for="Notes" class="form-control" rows="3"></textarea>
                                 <span asp-validation-for="Notes" class="text-danger"></span>
                             </div>
+                            <div class="col-12">
+                                <div class="form-check">
+                                    <input asp-for="IsIncoming" class="form-check-input" id="IsIncoming" />
+                                    <label class="form-check-label fw-semibold" for="IsIncoming">
+                                        <i class="bi bi-truck me-1 text-warning"></i>Incoming / On Order
+                                    </label>
+                                </div>
+                                <small class="text-muted d-block mt-1">
+                                    Uncheck once the powder has been received to mark it as regular in-stock inventory.
+                                </small>
+                            </div>
                         </div>
                     </div>