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/ToolsController.cs

@@ -911,7 +911,7 @@ public class ToolsController : Controller
     /// <c>CompanyId</c> provides the multi-tenant isolation that global query filters would
     /// normally enforce for other entity types.
     /// </summary>
-    // GET: Tools/GetShopWorkers - For randomizer wheel
+    // GET: Tools/GetShopWorkers - Returns active company users for randomizer wheel
     [HttpGet]
     public async Task<IActionResult> GetShopWorkers()
     {