refactor: move GpuEvaluatorFactory to OpenNest.Gpu project

GPU factory logic belongs with the GPU implementation, not the UI.
Changed from internal to public and updated namespace to OpenNest.Gpu.

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

OpenNest.Gpu/GpuEvaluatorFactory.cs

@@ -0,0 +1,76 @@
+using System;
+using System.Diagnostics;
+using ILGPU;
+using ILGPU.Runtime;
+using OpenNest.Engine.BestFit;
+
+namespace OpenNest.Gpu
+{
+    public static class GpuEvaluatorFactory
+    {
+        private static bool _probed;
+        private static bool _gpuAvailable;
+        private static string _deviceName;
+
+        public static bool GpuAvailable
+        {
+            get
+            {
+                if (!_probed) Probe();
+                return _gpuAvailable;
+            }
+        }
+
+        public static string DeviceName
+        {
+            get
+            {
+                if (!_probed) Probe();
+                return _deviceName ?? "None";
+            }
+        }
+
+        public static IPairEvaluator Create(Drawing drawing, double spacing)
+        {
+            if (!GpuAvailable)
+                return null;
+
+            try
+            {
+                return new GpuPairEvaluator(drawing, spacing);
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"[GpuEvaluatorFactory] GPU evaluator failed: {ex.Message}");
+                return null;
+            }
+        }
+
+        private static void Probe()
+        {
+            _probed = true;
+
+            try
+            {
+                using var context = Context.CreateDefault();
+                foreach (var device in context.Devices)
+                {
+                    if (device.AcceleratorType == AcceleratorType.Cuda ||
+                        device.AcceleratorType == AcceleratorType.OpenCL)
+                    {
+                        _gpuAvailable = true;
+                        _deviceName = device.Name;
+                        Debug.WriteLine($"[GpuEvaluatorFactory] GPU found: {device.Name} ({device.AcceleratorType})");
+                        return;
+                    }
+                }
+
+                Debug.WriteLine("[GpuEvaluatorFactory] No GPU device found");
+            }
+            catch (Exception ex)
+            {
+                Debug.WriteLine($"[GpuEvaluatorFactory] GPU probe failed: {ex.Message}");
+            }
+        }
+    }
+}