refactor: move ProgramVariableManager to Core, add config file support

- Move ProgramVariable and ProgramVariableManager from
  OpenNest.Posts.Cincinnati to OpenNest.Core/CNC (namespace OpenNest.CNC)
  so they can be used internally in nest programs
- Add parameterless constructor to CincinnatiPostProcessor that loads
  config from a .json file next to the DLL (creates defaults on first run)
- Enums serialize as readable strings (e.g., "Inches", "ControllerSide")
- Config file: OpenNest.Posts.Cincinnati.json in the Posts/ directory

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Tests/Cincinnati/CincinnatiPostProcessorTests.cs

@@ -1,5 +1,7 @@
 using System.IO;
 using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 using OpenNest.CNC;
 using OpenNest.Geometry;
 using OpenNest.Posts.Cincinnati;
@@ -96,6 +98,47 @@ public class CincinnatiPostProcessorTests
         }
     }
 
+    [Fact]
+    public void Config_RoundTripsAsJson()
+    {
+        var config = new CincinnatiPostConfig
+        {
+            ConfigurationName = "CL940_CORONA",
+            DefaultLibraryFile = "MS135N2PANEL.lib",
+            PostedUnits = Units.Inches,
+            KerfCompensation = KerfMode.ControllerSide,
+            UseAntiDive = true
+        };
+
+        var opts = new JsonSerializerOptions
+        {
+            WriteIndented = true,
+            Converters = { new JsonStringEnumConverter() }
+        };
+        var json = JsonSerializer.Serialize(config, opts);
+        var deserialized = JsonSerializer.Deserialize<CincinnatiPostConfig>(json, opts);
+
+        Assert.Equal("CL940_CORONA", deserialized.ConfigurationName);
+        Assert.Equal("MS135N2PANEL.lib", deserialized.DefaultLibraryFile);
+        Assert.Equal(Units.Inches, deserialized.PostedUnits);
+        Assert.Equal(KerfMode.ControllerSide, deserialized.KerfCompensation);
+        Assert.True(deserialized.UseAntiDive);
+
+        // Enums serialize as strings
+        Assert.Contains("\"Inches\"", json);
+        Assert.Contains("\"ControllerSide\"", json);
+    }
+
+    [Fact]
+    public void ParameterlessConstructor_LoadsOrCreatesConfig()
+    {
+        // The parameterless constructor reads from a .json file next to the assembly,
+        // or creates defaults if none exists. Either way, Config should be non-null.
+        var post = new CincinnatiPostProcessor();
+        Assert.NotNull(post.Config);
+        Assert.Equal("CL940", post.Config.ConfigurationName);
+    }
+
     private static Nest CreateTestNest()
     {
         var nest = new Nest("TestNest");

OpenNest.Tests/Cincinnati/CincinnatiPreambleWriterTests.cs

@@ -1,5 +1,6 @@
 using System.IO;
 using System.Text;
+using OpenNest.CNC;
 using OpenNest.Posts.Cincinnati;
 
 namespace OpenNest.Tests.Cincinnati;

OpenNest.Tests/Cincinnati/ProgramVariableManagerTests.cs

@@ -1,4 +1,4 @@
-using OpenNest.Posts.Cincinnati;
+using OpenNest.CNC;
 
 namespace OpenNest.Tests.Cincinnati;