Restructure project layout to flatten directory structure

Move all projects from Source/ to repository root for simpler navigation.
- Remove External/ dependency DLLs (will use NuGet packages)
- Remove Installer/ NSIS script
- Replace PartCollection/PlateCollection with ObservableList
- Add packages.config for NuGet dependencies

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

OpenNest/MainApp.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Runtime.InteropServices;
+using System.Windows.Forms;
+using OpenNest.Forms;
+
+namespace OpenNest
+{
+    internal static class MainApp
+    {
+        /// <summary>
+        /// The main entry point for the application.
+        /// </summary>
+        [STAThread]
+        private static void Main()
+        {
+            if (Environment.OSVersion.Version.Major >= 6)
+                SetProcessDPIAware();
+
+            Application.EnableVisualStyles();
+            Application.SetCompatibleTextRenderingDefault(false);
+            Application.Run(new MainForm());
+        }
+
+        [DllImport("user32.dll")]
+        private static extern bool SetProcessDPIAware();
+    }
+}