ASP.NET Core: Strongly-typed helpers migration and CSS consolidation

- Migrated to strongly-typed DataGrid<Employee> with lambda expressions
- Replaced AddSimple with AddSimpleFor(m => m.Property)
- Replaced Add with AddFor(m => m.Property) for columns
- Created Employee.cs model (renamed from SampleOrder.cs)
- Updated SampleData.cs with 9 employees matching other frameworks
- Removed SampleDataController.cs (using static data)
- Created separate Razor partial views: _CellTemplate.cshtml, _EditCellTemplate.cshtml
- Consolidated CSS from jQuery to Site.css with kebab-case naming
- Removed inline styles from Index.cshtml
- Added Nuget.config for DevExpress feed
- Removed nested ASP.NET Core/ folder structure
- Removed orig_ files
- Build passing with 0 errors (only DX license warnings)

Author: artem-kurchenko

ASP.NET Core/ASP.NET Core/Controllers/orig_HomeController.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace ASP_NET_Core.Models;
+
+public class Employee
+{
+    public int ID { get; set; }
+    public string FirstName { get; set; }
+    public string LastName { get; set; }
+    public string Prefix { get; set; }
+    public string Position { get; set; }
+    public string Picture { get; set; }
+    public DateTime BirthDate { get; set; }
+    public DateTime HireDate { get; set; }
+    public string Notes { get; set; }
+    public string Address { get; set; }
+}