feat(api): add NestStrategy, NestRequestPart, NestRequest

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

OpenNest.Api/NestRequestPart.cs

@@ -0,0 +1,9 @@
+namespace OpenNest.Api;
+
+public class NestRequestPart
+{
+    public string DxfPath { get; init; }
+    public int Quantity { get; init; } = 1;
+    public bool AllowRotation { get; init; } = true;
+    public int Priority { get; init; } = 0;
+}