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.Infrastructure/Repositories/UnitOfWork.cs

@@ -84,6 +84,7 @@ public class UnitOfWork : IUnitOfWork
     // Product Catalog
     private IRepository<CatalogCategory>? _catalogCategories;
     private IRepository<CatalogItem>? _catalogItems;
+    private IRepository<CatalogPriceCheckReport>? _catalogPriceCheckReports;
 
     // Notifications
     private IRepository<NotificationLog>? _notificationLogs;
@@ -344,6 +345,10 @@ public class UnitOfWork : IUnitOfWork
     public IRepository<CatalogItem> CatalogItems =>
         _catalogItems ??= new Repository<CatalogItem>(_context);
 
+    /// <summary>Repository for <see cref="CatalogPriceCheckReport"/> AI price-check results archived per company.</summary>
+    public IRepository<CatalogPriceCheckReport> CatalogPriceCheckReports =>
+        _catalogPriceCheckReports ??= new Repository<CatalogPriceCheckReport>(_context);
+
     // Notifications
     /// <summary>Repository for <see cref="NotificationLog"/> outbound notification audit records; tenant-filtered with soft delete.</summary>
     public IRepository<NotificationLog> NotificationLogs =>