Remove ShopWorker entity and migrate worker identity to ApplicationUser

Removes the ShopWorker and ShopWorkerRoleCost entities, all related DTOs,
mappings, controllers, views, and import/export paths. Worker identity is
now handled entirely through ApplicationUser with per-user LaborCostPerHour.
ShopWorkerRoleCosts table remains in production pending manual data migration.

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

src/PowderCoating.Web/Controllers/DataExportController.cs

@@ -712,7 +712,7 @@ public class DataExportController : Controller
 
     /// <summary>
     /// Returns the requested sheet names sorted into the canonical export order
-    /// (Customers → Jobs → Quotes → Invoices → Inventory → Equipment → Vendors → ShopWorkers → Users).
+    /// (Customers → Jobs → Quotes → Invoices → Inventory → Equipment → Vendors → Users).
     /// This ensures that the workbook and ZIP archive always have a predictable, logical layout
     /// regardless of the order the administrator checked the boxes on the form.
     /// Any sheet name not in the canonical list is silently ignored.