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/Entities/JobTimeEntry.cs

@@ -3,7 +3,6 @@ namespace PowderCoating.Core.Entities;
 public class JobTimeEntry : BaseEntity
 {
     public int JobId { get; set; }
-    public int? ShopWorkerId { get; set; }       // legacy — kept for entries created before user migration
     public string? UserId { get; set; }           // FK to AspNetUsers
     public string? UserDisplayName { get; set; }  // snapshot of worker name at entry creation time
     public DateTime WorkDate { get; set; }
@@ -13,5 +12,4 @@ public class JobTimeEntry : BaseEntity
 
     // Navigation
     public virtual Job Job { get; set; } = null!;
-    public virtual ShopWorker? Worker { get; set; }  // nullable — only populated for legacy entries
 }