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.Core/Interfaces/IUnitOfWork.cs

@@ -54,9 +54,7 @@ public interface IUnitOfWork : IDisposable
     IRepository<AppointmentStatusLookup> AppointmentStatusLookups { get; }
     IRepository<AppointmentTypeLookup> AppointmentTypeLookups { get; }
     IRepository<PrepService> PrepServices { get; }
-    IRepository<ShopWorker> ShopWorkers { get; }
-    IRepository<ShopWorkerRoleCost> ShopWorkerRoleCosts { get; }
-    IRepository<ReworkRecord> ReworkRecords { get; }
+IRepository<ReworkRecord> ReworkRecords { get; }
     IRepository<Refund> Refunds { get; }
     IRepository<CreditMemo> CreditMemos { get; }
     IRepository<CreditMemoApplication> CreditMemoApplications { get; }