feat: add GPU status indicator and device probe

- GpuEvaluatorFactory probes for CUDA/OpenCL devices at startup
- Status bar shows "GPU : <device name>" (green) or "GPU : None (CPU)" (gray)
- Factory skips GPU evaluator creation entirely when no device found
- Logs actual exception message on failure for debugging

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

OpenNest/Forms/MainForm.Designer.cs

@@ -59,6 +59,7 @@
             this.mnuViewZoomIn = new System.Windows.Forms.ToolStripMenuItem();
             this.mnuViewZoomOut = new System.Windows.Forms.ToolStripMenuItem();
             this.mnuTools = new System.Windows.Forms.ToolStripMenuItem();
+            this.mnuToolsBestFitViewer = new System.Windows.Forms.ToolStripMenuItem();
             this.mnuToolsMeasureArea = new System.Windows.Forms.ToolStripMenuItem();
             this.mnuToolsAlign = new System.Windows.Forms.ToolStripMenuItem();
             this.mnuToolsAlignLeft = new System.Windows.Forms.ToolStripMenuItem();
@@ -129,6 +130,7 @@
             this.plateIndexStatusLabel = new System.Windows.Forms.ToolStripStatusLabel();
             this.plateSizeStatusLabel = new System.Windows.Forms.ToolStripStatusLabel();
             this.plateQtyStatusLabel = new System.Windows.Forms.ToolStripStatusLabel();
+            this.gpuStatusLabel = new System.Windows.Forms.ToolStripStatusLabel();
             this.toolStrip1 = new System.Windows.Forms.ToolStrip();
             this.btnNew = new System.Windows.Forms.ToolStripButton();
             this.btnOpen = new System.Windows.Forms.ToolStripButton();
@@ -412,6 +414,7 @@
             // 
             this.mnuTools.DropDownItems.AddRange(new System.Windows.Forms.ToolStripItem[] {
             this.mnuToolsMeasureArea,
+            this.mnuToolsBestFitViewer,
             this.mnuToolsAlign,
             this.toolStripMenuItem14,
             this.mnuSetOffsetIncrement,
@@ -428,7 +431,14 @@
             this.mnuToolsMeasureArea.Size = new System.Drawing.Size(214, 22);
             this.mnuToolsMeasureArea.Text = "Measure Area";
             this.mnuToolsMeasureArea.Click += new System.EventHandler(this.MeasureArea_Click);
-            // 
+            //
+            // mnuToolsBestFitViewer
+            //
+            this.mnuToolsBestFitViewer.Name = "mnuToolsBestFitViewer";
+            this.mnuToolsBestFitViewer.Size = new System.Drawing.Size(214, 22);
+            this.mnuToolsBestFitViewer.Text = "Best-Fit Viewer";
+            this.mnuToolsBestFitViewer.Click += new System.EventHandler(this.BestFitViewer_Click);
+            //
             // mnuToolsAlign
             // 
             this.mnuToolsAlign.DropDownItems.AddRange(new System.Windows.Forms.ToolStripItem[] {
@@ -909,7 +919,8 @@
             this.spacerLabel,
             this.plateIndexStatusLabel,
             this.plateSizeStatusLabel,
-            this.plateQtyStatusLabel});
+            this.plateQtyStatusLabel,
+            this.gpuStatusLabel});
             this.statusStrip1.Location = new System.Drawing.Point(0, 543);
             this.statusStrip1.Name = "statusStrip1";
             this.statusStrip1.Size = new System.Drawing.Size(1098, 24);
@@ -961,7 +972,14 @@
             this.plateQtyStatusLabel.Padding = new System.Windows.Forms.Padding(5, 0, 5, 0);
             this.plateQtyStatusLabel.Size = new System.Drawing.Size(55, 19);
             this.plateQtyStatusLabel.Text = "Qty : 0";
-            // 
+            //
+            // gpuStatusLabel
+            //
+            this.gpuStatusLabel.BorderSides = System.Windows.Forms.ToolStripStatusLabelBorderSides.Left;
+            this.gpuStatusLabel.Name = "gpuStatusLabel";
+            this.gpuStatusLabel.Padding = new System.Windows.Forms.Padding(5, 0, 5, 0);
+            this.gpuStatusLabel.Size = new System.Drawing.Size(55, 19);
+            //
             // toolStrip1
             // 
             this.toolStrip1.AutoSize = false;
@@ -1287,7 +1305,9 @@
         private System.Windows.Forms.ToolStripMenuItem manualSequenceToolStripMenuItem;
         private System.Windows.Forms.ToolStripMenuItem autoSequenceAllPlatesToolStripMenuItem;
         private System.Windows.Forms.ToolStripMenuItem mnuToolsMeasureArea;
+        private System.Windows.Forms.ToolStripMenuItem mnuToolsBestFitViewer;
         private System.Windows.Forms.ToolStripButton btnSaveAs;
         private System.Windows.Forms.ToolStripMenuItem centerPartsToolStripMenuItem;
+        private System.Windows.Forms.ToolStripStatusLabel gpuStatusLabel;
     }
 }

OpenNest/Forms/MainForm.cs

@@ -39,6 +39,7 @@ namespace OpenNest.Forms
             LoadPosts();
             EnableCheck();
             UpdateStatus();
+            UpdateGpuStatus();
         }
 
         private string GetNestName(DateTime date, int id)
@@ -191,6 +192,20 @@ namespace OpenNest.Forms
             UpdatePlateStatus();
         }
 
+        private void UpdateGpuStatus()
+        {
+            if (GpuEvaluatorFactory.GpuAvailable)
+            {
+                gpuStatusLabel.Text = $"GPU : {GpuEvaluatorFactory.DeviceName}";
+                gpuStatusLabel.ForeColor = Color.DarkGreen;
+            }
+            else
+            {
+                gpuStatusLabel.Text = "GPU : None (CPU)";
+                gpuStatusLabel.ForeColor = Color.Gray;
+            }
+        }
+
         private void UpdateLocationMode()
         {
             if (activeForm == null)

OpenNest/GpuEvaluatorFactory.cs

@@ -1,4 +1,7 @@
+using System;
 using System.Diagnostics;
+using ILGPU;
+using ILGPU.Runtime;
 using OpenNest.Engine.BestFit;
 using OpenNest.Gpu;
 
@@ -6,17 +9,69 @@ namespace OpenNest
 {
     internal 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
+            catch (Exception ex)
             {
-                Debug.WriteLine("[GpuEvaluatorFactory] GPU not available, falling back to CPU");
+                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}");
+            }
+        }
     }
 }