Fix oven batch conversion, invoice quantity, AI photo pricing, and enforce pricing flag propagation

- Carry OvenBatches/OvenCycleMinutes from Quote → Job entity (was missing fields; all job pricing recalcs hardcoded 1/null)
- Fix invoice creation from job always showing Quantity=1 (was using TotalPrice as UnitPrice with qty 1)
- Add IsAiItem to JobItem + migration; map in all 3 JobItemAssemblyService.CreateJobItem overloads so AI photo jobs no longer double-price on first edit after quote→job conversion
- Propagate IsAiItem through all existingItemsData JSON blocks in Jobs views (Edit, EditItems, Create) so the wizard preserves AI routing on re-edit
- Add PricingRoutingFlags_ExistOnBothQuoteItemAndJobItem structural test + 3 behavioral IsAiItem tests to JobItemAssemblyServiceTests
- Consolidate item wizard partials (_ItemWizardModal, _SqFtCalculatorModal) and item-wizard.css into shared locations
- Document pricing flag propagation checklist in CLAUDE.md

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

src/PowderCoating.Web/Controllers/InvoicesController.cs

@@ -396,13 +396,13 @@ public class InvoicesController : Controller
 
                     dto.InvoiceItems.Add(new CreateInvoiceItemDto
                     {
-                        SourceJobItemId = item.Id,
-                        Description = item.Description ?? "Powder Coating",
-                        Quantity = 1,
-                        UnitPrice = item.TotalPrice,
-                        TotalPrice = item.TotalPrice,
-                        ColorName = item.ColorName,
-                        DisplayOrder = order++,
+                        SourceJobItemId  = item.Id,
+                        Description      = item.Description ?? "Powder Coating",
+                        Quantity         = item.Quantity > 0 ? item.Quantity : 1,
+                        UnitPrice        = item.UnitPrice,
+                        TotalPrice       = item.TotalPrice,
+                        ColorName        = item.ColorName,
+                        DisplayOrder     = order++,
                         RevenueAccountId = revenueAccountId
                     });
                 }