feat(cincinnati): seed material library defaults and add selector dropdown

Adds the full Cincinnati material/etch library list as the committed
default config (seeded into Posts/ on build only when no runtime config
exists), plus a Selected Library override in the PropertyGrid backed by
a TypeConverter that populates from MaterialLibraries. MainForm calls
the new IPostProcessorNestAware hook before showing the config so the
dropdown opens preselected to the best match by nest material and
nearest thickness.

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

OpenNest.Posts.Cincinnati/CincinnatiPostProcessor.cs

@@ -9,7 +9,7 @@ using OpenNest.CNC;
 
 namespace OpenNest.Posts.Cincinnati
 {
-    public sealed class CincinnatiPostProcessor : IConfigurablePostProcessor, IMaterialProvidingPostProcessor
+    public sealed class CincinnatiPostProcessor : IConfigurablePostProcessor, IPostProcessorNestAware, IMaterialProvidingPostProcessor
     {
         private static readonly JsonSerializerOptions JsonOptions = new()
         {
@@ -35,6 +35,13 @@ namespace OpenNest.Posts.Cincinnati
                 .Where(s => !string.IsNullOrWhiteSpace(s));
         }
 
+        public void PrepareForNest(Nest nest)
+        {
+            var materialName = nest?.Material?.Name ?? "";
+            var thickness = nest?.Thickness ?? 0.0;
+            Config.SelectedLibrary = Config.FindBestLibrary(materialName, thickness);
+        }
+
         public CincinnatiPostProcessor()
         {
             var configPath = GetConfigPath();
@@ -138,7 +145,8 @@ namespace OpenNest.Posts.Cincinnati
             // Part sub-programs (if enabled)
             if (subprogramEntries != null)
             {
-                var partSubWriter = new CincinnatiPartSubprogramWriter(Config);
+                var partSubWriter = new CincinnatiPartSubprogramWriter(Config,
+                    holeMapping.Count > 0 ? holeMapping : null);
                 var sheetDiagonal = firstPlate != null
                     ? System.Math.Sqrt(firstPlate.Size.Width * firstPlate.Size.Width
                         + firstPlate.Size.Length * firstPlate.Size.Length)