Add three-layer feature gating for AI Catalog Price Check

Adds platform-level, plan-level (Enterprise only), and per-company
toggles for the AI Catalog Price Check feature. Includes:
- Company.AiCatalogPriceCheckEnabled per-company flag
- SubscriptionPlanConfig.AllowAiCatalogPriceCheck plan-level flag
- PlatformSetting 'AiCatalogPriceCheckEnabled' global kill switch
- IPlatformSettingsService.GetBoolAsync helper
- ISubscriptionService.CanUseAiCatalogPriceCheckAsync
- UI controls in Companies/Edit, PlatformSubscription/Edit+Index,
  and SubscriptionManagement/Manage
- Migration AddAiCatalogPriceCheckGating applied

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

src/PowderCoating.Web/Controllers/PlatformSubscriptionController.cs

@@ -63,6 +63,7 @@ public class PlatformSubscriptionController : Controller
             AllowAccounting = c.AllowAccounting,
             AllowAiPhotoQuotes = c.AllowAiPhotoQuotes,
             AllowAiInventoryAssist = c.AllowAiInventoryAssist,
+            AllowAiCatalogPriceCheck = c.AllowAiCatalogPriceCheck,
             IsActive = c.IsActive,
             SortOrder = c.SortOrder
         }).ToList();
@@ -102,6 +103,7 @@ public class PlatformSubscriptionController : Controller
             AllowAccounting = config.AllowAccounting,
             AllowAiPhotoQuotes = config.AllowAiPhotoQuotes,
             AllowAiInventoryAssist = config.AllowAiInventoryAssist,
+            AllowAiCatalogPriceCheck = config.AllowAiCatalogPriceCheck,
             IsActive = config.IsActive
         };
 
@@ -146,6 +148,7 @@ public class PlatformSubscriptionController : Controller
         config.AllowAccounting = dto.AllowAccounting;
         config.AllowAiPhotoQuotes = dto.AllowAiPhotoQuotes;
         config.AllowAiInventoryAssist = dto.AllowAiInventoryAssist;
+        config.AllowAiCatalogPriceCheck = dto.AllowAiCatalogPriceCheck;
         config.IsActive = dto.IsActive;
 
         await _unitOfWork.SubscriptionPlanConfigs.UpdateAsync(config);