refactor(core): drop System.Drawing.Common and fix CutParameters namespace

Core only uses System.Drawing.Color, which ships in the shared framework, so
the System.Drawing.Common package (Windows-only beyond primitives) was an
unneeded dependency of the cross-platform domain library. The desktop app
keeps its own reference.

CutParameters lives in OpenNest.Core but declared namespace OpenNest.Api,
forcing Core and desktop files to import the Api namespace for a Core type.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Core/CutParameters.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace OpenNest.Api;
+namespace OpenNest;
 
 public class CutParameters
 {

OpenNest.Core/OpenNest.Core.csproj

@@ -10,6 +10,5 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Clipper2" Version="2.0.0" />
-    <PackageReference Include="System.Drawing.Common" Version="8.0.10" />
   </ItemGroup>
 </Project>

OpenNest.Core/Timing.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Linq;
-using OpenNest.Api;
 using OpenNest.CNC;
 using OpenNest.Converters;
 using OpenNest.Geometry;

OpenNest.Tests/Api/CutParametersTests.cs

@@ -1,5 +1,3 @@
-using OpenNest.Api;
-
 namespace OpenNest.Tests.Api;
 
 public class CutParametersTests

OpenNest.Tests/TimingTests.cs

@@ -1,4 +1,3 @@
-using OpenNest.Api;
 using OpenNest.Geometry;
 
 namespace OpenNest.Tests;

OpenNest/Forms/CutParametersForm.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Windows.Forms;
-using OpenNest.Api;
 
 namespace OpenNest.Forms
 {

OpenNest/Forms/EditNestForm.cs

@@ -6,7 +6,6 @@ using System.IO;
 using System.Linq;
 using System.Windows.Forms;
 using OpenNest.Actions;
-using OpenNest.Api;
 using OpenNest.CNC.CuttingStrategy;
 using OpenNest.Collections;
 using OpenNest.Controls;

OpenNest/Forms/TimingForm.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Windows.Forms;
-using OpenNest.Api;
 
 namespace OpenNest.Forms
 {