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/CompanyOperatingCosts.cs

@@ -13,6 +13,14 @@ namespace PowderCoating.Core.Entities
         [Range(0, 10000)]
         public decimal StandardLaborRate { get; set; }
 
+        /// <summary>
+        /// Actual labor cost per hour (wages + burden) used exclusively for internal job costing and profit/margin display.
+        /// This is NOT the billing rate — it should reflect what you actually pay workers.
+        /// When null, the costing engine defaults to 20% of StandardLaborRate.
+        /// </summary>
+        [Range(0, 10000)]
+        public decimal? LaborCostPerHour { get; set; }
+
         // Additional Coat Labor Percentage (percentage of base labor for each additional coat beyond the first)
         [Range(0, 100)]
         public decimal AdditionalCoatLaborPercent { get; set; } = 30m;