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/SubscriptionManagementController.cs

@@ -462,12 +462,14 @@ public class SubscriptionManagementController : Controller
     /// <param name="id">Primary key of the company to update.</param>
     /// <param name="aiPhotoQuotesEnabled">Whether AI photo quoting is enabled for this company.</param>
     /// <param name="aiInventoryAssistEnabled">Whether AI inventory assistance is enabled for this company.</param>
+    /// <param name="aiCatalogPriceCheckEnabled">Whether AI catalog price check is enabled for this company.</param>
     /// <param name="maxAiPhotoQuotesPerMonthOverride">Monthly AI photo quote limit override; 0 = plan default.</param>
     [HttpPost, ValidateAntiForgeryToken]
     public async Task<IActionResult> UpdateFeatureFlags(
         int id,
         bool aiPhotoQuotesEnabled,
         bool aiInventoryAssistEnabled,
+        bool aiCatalogPriceCheckEnabled,
         int? maxAiPhotoQuotesPerMonthOverride)
     {
         var company = await _db.Companies.IgnoreQueryFilters().FirstOrDefaultAsync(c => c.Id == id);
@@ -475,6 +477,7 @@ public class SubscriptionManagementController : Controller
 
         company.AiPhotoQuotesEnabled = aiPhotoQuotesEnabled;
         company.AiInventoryAssistEnabled = aiInventoryAssistEnabled;
+        company.AiCatalogPriceCheckEnabled = aiCatalogPriceCheckEnabled;
         company.MaxAiPhotoQuotesPerMonthOverride = NullIfZero(maxAiPhotoQuotesPerMonthOverride);
         company.UpdatedAt = DateTime.UtcNow;
         company.UpdatedBy = User.Identity?.Name;