feat: add material library resolution, assist gas support, and UI fixes

- Add MaterialLibraryResolver for Cincinnati post processor to resolve
  G89 library files from material/thickness/gas configuration
- Add Nest.AssistGas property with serialization support in nest format
- Add etch library support with separate gas configuration
- Fix CutOff tests to match AwayFromOrigin default cut direction
- Fix plate info label not updating after ResizePlateToFitParts
- Add cutoff and remnants toolbar button icons

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

OpenNest.Posts.Cincinnati/MaterialLibraryResolver.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace OpenNest.Posts.Cincinnati;
+
+public sealed class MaterialLibraryResolver
+{
+    private const double ThicknessTolerance = 0.001;
+
+    private readonly List<MaterialLibraryEntry> _materialLibraries;
+    private readonly List<EtchLibraryEntry> _etchLibraries;
+
+    public MaterialLibraryResolver(CincinnatiPostConfig config)
+    {
+        _materialLibraries = config.MaterialLibraries ?? new List<MaterialLibraryEntry>();
+        _etchLibraries = config.EtchLibraries ?? new List<EtchLibraryEntry>();
+    }
+
+    public string ResolveCutLibrary(string materialName, double thickness, string gas)
+    {
+        var entry = _materialLibraries.FirstOrDefault(e =>
+            string.Equals(e.Material, materialName, StringComparison.OrdinalIgnoreCase) &&
+            System.Math.Abs(e.Thickness - thickness) <= ThicknessTolerance &&
+            string.Equals(e.Gas, gas, StringComparison.OrdinalIgnoreCase));
+
+        return entry?.Library ?? "";
+    }
+
+    public string ResolveEtchLibrary(string gas)
+    {
+        var entry = _etchLibraries.FirstOrDefault(e =>
+            string.Equals(e.Gas, gas, StringComparison.OrdinalIgnoreCase));
+
+        return entry?.Library ?? "";
+    }
+
+    public static string ResolveGas(Nest nest, CincinnatiPostConfig config)
+    {
+        return !string.IsNullOrEmpty(nest.AssistGas) ? nest.AssistGas : config.DefaultAssistGas;
+    }
+}