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/ApplicationUser.cs

@@ -58,7 +58,14 @@ public class ApplicationUser : IdentityUser
 
     public string? SidebarColor { get; set; } = "ocean";
     public string? Notes { get; set; }
-    
+
+    /// <summary>
+    /// Per-worker labor cost per hour used for job costing profit/margin calculations.
+    /// Overrides the company-level LaborCostPerHour when set.
+    /// Leave null to use the company default.
+    /// </summary>
+    public decimal? LaborCostPerHour { get; set; }
+
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
     public DateTime? UpdatedAt { get; set; }
     public DateTime? LastLoginDate { get; set; }