feat: add IConfigurablePostProcessor interface and implement in Cincinnati post

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

OpenNest.Core/IConfigurablePostProcessor.cs

@@ -0,0 +1,9 @@
+namespace OpenNest
+{
+    public interface IConfigurablePostProcessor : IPostProcessor
+    {
+        object Config { get; }
+
+        void SaveConfig();
+    }
+}

OpenNest.Posts.Cincinnati/CincinnatiPostProcessor.cs

@@ -9,7 +9,7 @@ using OpenNest.CNC;
 
 namespace OpenNest.Posts.Cincinnati
 {
-    public sealed class CincinnatiPostProcessor : IPostProcessor
+    public sealed class CincinnatiPostProcessor : IConfigurablePostProcessor
     {
         private static readonly JsonSerializerOptions JsonOptions = new()
         {
@@ -23,6 +23,8 @@ namespace OpenNest.Posts.Cincinnati
 
         public CincinnatiPostConfig Config { get; }
 
+        object IConfigurablePostProcessor.Config => Config;
+
         public CincinnatiPostProcessor()
         {
             var configPath = GetConfigPath();

OpenNest.Tests/Cincinnati/CincinnatiPostProcessorTests.cs

@@ -121,6 +121,17 @@ public class CincinnatiPostProcessorTests
         Assert.Equal("OpenNest", pp.Author);
     }
 
+    [Fact]
+    public void Post_ImplementsIConfigurablePostProcessor()
+    {
+        var post = new CincinnatiPostProcessor(new CincinnatiPostConfig());
+        var configurable = post as IConfigurablePostProcessor;
+
+        Assert.NotNull(configurable);
+        Assert.NotNull(configurable.Config);
+        Assert.IsType<CincinnatiPostConfig>(configurable.Config);
+    }
+
     [Fact]
     public void Post_SkipsEmptyPlates()
     {