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.Application/Interfaces/IPlatformSettingsService.cs

@@ -5,6 +5,7 @@ namespace PowderCoating.Application.Interfaces;
 public interface IPlatformSettingsService
 {
     Task<string?> GetAsync(string key);
+    Task<bool> GetBoolAsync(string key, bool defaultValue = false);
     Task SetAsync(string key, string? value, string? updatedBy = null);
     Task<IReadOnlyList<PlatformSetting>> GetAllAsync();
 }