refactor: move CutParameters to OpenNest.Api namespace with new properties

Relocates CutParameters from OpenNest namespace to OpenNest.Api, adds
LeadInLength and PostProcessor properties, and provides a typed Default
factory. Updates Timing.cs, the WinForms project reference, and the three
consuming forms to resolve the type from the new namespace.

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

OpenNest.Tests/Api/CutParametersTests.cs

@@ -0,0 +1,35 @@
+using OpenNest.Api;
+
+namespace OpenNest.Tests.Api;
+
+public class CutParametersTests
+{
+    [Fact]
+    public void Default_HasExpectedValues()
+    {
+        var cp = CutParameters.Default;
+
+        Assert.Equal(100, cp.Feedrate);
+        Assert.Equal(300, cp.RapidTravelRate);
+        Assert.Equal(TimeSpan.FromSeconds(0.5), cp.PierceTime);
+        Assert.Equal(Units.Inches, cp.Units);
+    }
+
+    [Fact]
+    public void Properties_AreSettable()
+    {
+        var cp = new CutParameters
+        {
+            Feedrate = 200,
+            RapidTravelRate = 500,
+            PierceTime = TimeSpan.FromSeconds(1.0),
+            LeadInLength = 0.25,
+            PostProcessor = "CL-707",
+            Units = Units.Millimeters
+        };
+
+        Assert.Equal(200, cp.Feedrate);
+        Assert.Equal(0.25, cp.LeadInLength);
+        Assert.Equal("CL-707", cp.PostProcessor);
+    }
+}