Rename SawCut library to CutList.Core

Rename the core library project from SawCut to CutList.Core for consistent
branding across the solution. This includes:
- Rename project folder and .csproj file
- Update namespace from SawCut to CutList.Core
- Update all using statements and project references

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CutList.Core/Nesting/IEngine.cs

@@ -0,0 +1,9 @@
+using System.Collections.Generic;
+
+namespace CutList.Core.Nesting
+{
+    public interface IEngine
+    {
+        Result Pack(List<BinItem> items);
+    }
+}