Add AI Catalog Price Check feature

Claude reviews every active catalog item against the shop's own operating costs
and returns a per-item verdict (below-cost / thin-margin / high / ok) with a
suggested price range, cost floor, and assumptions.

- New entity: CatalogPriceCheckReport (JSON blob, archived per company)
- New service: IAiCatalogPriceCheckService / AiCatalogPriceCheckService
  batches items 25 at a time to stay within model context limits
- Two new controller actions: GET AiPriceCheck (view report) + POST RunAiPriceCheck
- AiPriceCheck view: summary cards (counts by verdict), color-coded item cards
  with Edit Price link, assumptions detail, and loading spinner on submit
- AI Price Check button added to catalog Index header
- Migration AddCatalogPriceCheckReport applied

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

src/PowderCoating.Core/Interfaces/IUnitOfWork.cs

@@ -63,6 +63,7 @@ public interface IUnitOfWork : IDisposable
     // Product Catalog
     IRepository<CatalogCategory> CatalogCategories { get; }
     IRepository<CatalogItem> CatalogItems { get; }
+    IRepository<CatalogPriceCheckReport> CatalogPriceCheckReports { get; }
 
     // Oven Scheduling
     IRepository<OvenBatch> OvenBatches { get; }