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/LayoutPart.cs

@@ -0,0 +1,202 @@
+using System.Drawing;
+using System.Drawing.Drawing2D;
+using System.Windows.Forms;
+using OpenNest.Controls;
+
+namespace OpenNest
+{
+    public class LayoutPart : IPart
+    {
+        private static Font programIdFont;
+        private static Color selectedColor;
+        private static Pen selectedPen;
+        private static Brush selectedBrush;
+
+        private Color color;
+        private Brush brush;
+        private Pen pen;
+
+        public readonly Part BasePart;
+
+        static LayoutPart()
+        {
+            programIdFont = new Font(SystemFonts.DefaultFont, FontStyle.Bold | FontStyle.Underline);
+            SelectedColor = Color.FromArgb(90, 150, 200, 255);
+        }
+
+        private LayoutPart(Part part)
+        {
+            this.BasePart = part;
+
+            if (part.BaseDrawing.Color.IsEmpty)
+                part.BaseDrawing.Color = Color.FromArgb(130, 204, 130);
+
+            Color = part.BaseDrawing.Color;
+        }
+
+        internal bool IsDirty { get; set; }
+
+        public bool IsSelected { get; set; }
+        
+        public GraphicsPath Path { get; private set; }
+
+        public Color Color
+        {
+            get { return color; }
+            set
+            {
+                color = value;
+
+                if (brush != null)
+                    brush.Dispose();
+
+                brush = new SolidBrush(value);
+
+                if (pen != null)
+                    pen.Dispose();
+
+                pen = new Pen(ControlPaint.Dark(value));
+            }
+        }
+
+        public void Draw(Graphics g)
+        {
+            if (IsSelected)
+            {
+                g.FillPath(selectedBrush, Path);
+                g.DrawPath(selectedPen, Path);
+            }
+            else
+            {
+                g.FillPath(brush, Path);
+                g.DrawPath(pen, Path);
+            }
+        }
+
+        public void Draw(Graphics g, string id)
+        {
+            if (IsSelected)
+            {
+                g.FillPath(selectedBrush, Path);
+                g.DrawPath(selectedPen, Path);
+            }
+            else
+            {
+                g.FillPath(brush, Path);
+                g.DrawPath(pen, Path);
+            }
+
+            var pt = Path.PointCount > 0 ? Path.PathPoints[0] : PointF.Empty;
+
+            g.DrawString(id, programIdFont, Brushes.Black, pt.X, pt.Y);
+        }
+
+        public void Update(DrawControl plateView)
+        {
+            Path = GraphicsHelper.GetGraphicsPath(BasePart.Program, BasePart.Location);
+            Path.Transform(plateView.Matrix);
+            IsDirty = false;
+        }
+
+        public static LayoutPart Create(Part part, PlateView plateView)
+        {
+            var layoutPart = new LayoutPart(part);
+            layoutPart.Update(plateView);
+
+            return layoutPart;
+        }
+
+        public static Color SelectedColor
+        {
+            get { return selectedColor; }
+            set
+            {
+                selectedColor = value;
+
+                if (selectedBrush != null)
+                    selectedBrush.Dispose();
+
+                selectedBrush = new SolidBrush(value);
+
+                if (selectedPen != null)
+                    selectedPen.Dispose();
+
+                selectedPen = new Pen(ControlPaint.Dark(value));
+            }
+        }
+
+        public Vector Location
+        {
+            get { return BasePart.Location; }
+            set
+            {
+                BasePart.Location = value;
+                IsDirty = true;
+            }
+        }
+
+        public double Rotation
+        {
+            get { return BasePart.Rotation; }
+        }
+
+        public void Rotate(double angle)
+        {
+            BasePart.Rotate(angle);
+            IsDirty = true;
+        }
+
+        public void Rotate(double angle, Vector origin)
+        {
+            BasePart.Rotate(angle, origin);
+            IsDirty = true;
+        }
+
+        public void Offset(double x, double y)
+        {
+            BasePart.Offset(x, y);
+            IsDirty = true;
+        }
+
+        public void Offset(Vector voffset)
+        {
+            BasePart.Offset(voffset);
+            IsDirty = true;
+        }
+
+        public Box BoundingBox
+        {
+            get { return BasePart.BoundingBox; }
+        }
+
+        public double Left
+        {
+            get { return BasePart.Left; }
+        }
+
+        public double Right
+        {
+            get { return BasePart.Right; }
+        }
+
+        public double Top
+        {
+            get { return BasePart.Top; }
+        }
+
+        public double Bottom
+        {
+            get { return BasePart.Bottom; }
+        }
+
+        public void UpdateBounds()
+        {
+            BasePart.UpdateBounds();
+        }
+
+        public void Update()
+        {
+            Color = BasePart.BaseDrawing.Color;
+        }
+    }
+}