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.Core/Entities/Job.cs

@@ -25,6 +25,10 @@ public class Job : BaseEntity
     // Selected oven (carried over from quote; null = company default rate)
     public int? OvenCostId { get; set; }
 
+    // Oven scheduling (carried over from quote)
+    public int OvenBatches { get; set; } = 1;
+    public int? OvenCycleMinutes { get; set; }
+
     // Pricing
     public decimal QuotedPrice { get; set; }
     public decimal FinalPrice { get; set; }