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/Entities/CatalogPriceCheckReport.cs

@@ -0,0 +1,20 @@
+namespace PowderCoating.Core.Entities
+{
+    /// <summary>
+    /// Stores the result of the most recent AI catalog price check run for a company.
+    /// ResultsJson holds the full per-item verdict array serialized as JSON, avoiding the
+    /// need for a wide per-item table while still persisting the report across sessions.
+    /// Only one report is kept per company — each new run overwrites the previous one.
+    /// </summary>
+    public class CatalogPriceCheckReport : BaseEntity
+    {
+        public DateTime RunAt { get; set; }
+        public int ItemsChecked { get; set; }
+
+        /// <summary>JSON-serialized List&lt;CatalogItemPriceVerdict&gt;.</summary>
+        public string ResultsJson { get; set; } = "[]";
+
+        /// <summary>Human-readable summary of the operating costs used for this run.</summary>
+        public string OperatingCostsSummary { get; set; } = string.Empty;
+    }
+}