feat: move PushDirection enum to OpenNest.Core

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

OpenNest.Core/OpenNest.Core.csproj

@@ -88,6 +88,7 @@
     <Compile Include="Converters\ConvertMode.cs" />
     <Compile Include="Nest.cs" />
     <Compile Include="Part.cs" />
+    <Compile Include="PushDirection.cs" />
     <Compile Include="Collections\ObservableList.cs" />
     <Compile Include="Plate.cs" />
     <Compile Include="CNC\Program.cs" />

OpenNest.Core/PushDirection.cs

@@ -0,0 +1,11 @@
+
+namespace OpenNest
+{
+    public enum PushDirection
+    {
+        Up,
+        Down,
+        Left,
+        Right
+    }
+}