feat(io): add Gravograph .CHR font reader with text-to-geometry

Add ChrFont, a reader for Gravograph .CHR engraving fonts, plus UI to
convert placed text into engraved geometry in the CAD converter.

The .CHR files are obfuscated with a single-byte XOR. Different
GravoStyle releases use different keys (0x2F in older versions, 0xCF in
the 7000 series, and others across the font library), so the key is
auto-detected from byte 1 of the file: the font name is ASCII stored as
UTF-16LE, so the high byte of its first character is 0x00 in plaintext
and the raw byte equals the key. This reads every font in a GravoStyle
install regardless of version, not just one hardcoded key.

UI: right-clicking a text item in EntityView raises TextConvertRequested;
CadConverterForm renders it via ChrFont with H/V alignment and adds the
result on an ENGRAVE layer.

Tests use Xunit.SkippableFact and a gitignored test-config.json so the
suite points at a local .CHR file without committing proprietary assets.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

OpenNest/Controls/EntityView.cs

@@ -40,6 +40,7 @@ namespace OpenNest.Controls
 
         public event EventHandler<Line> LinePicked;
         public event EventHandler PickCancelled;
+        public event EventHandler<CadText> TextConvertRequested;
 
         private bool isPickingBendLine;
         public bool IsPickingBendLine
@@ -76,6 +77,13 @@ namespace OpenNest.Controls
                 if (line != null)
                     LinePicked?.Invoke(this, line);
             }
+
+            if (e.Button == MouseButtons.Right)
+            {
+                var text = HitTestText(e.Location);
+                if (text != null)
+                    ShowTextContextMenu(text, e.Location);
+            }
         }
 
         protected override void OnPaint(PaintEventArgs e)
@@ -328,6 +336,41 @@ namespace OpenNest.Controls
             return bestLine;
         }
 
+        private CadText HitTestText(Point controlPoint)
+        {
+            if (Texts == null || Texts.Count == 0)
+                return null;
+
+            var worldPoint = PointControlToWorld(controlPoint);
+            var tolerance = LengthGuiToWorld(8);
+
+            foreach (var text in Texts)
+            {
+                if (string.IsNullOrEmpty(text.Value))
+                    continue;
+
+                var estimatedWidth = text.Height * text.Value.Length * 0.6;
+                var minX = text.Position.X - tolerance;
+                var maxX = text.Position.X + estimatedWidth + tolerance;
+                var minY = text.Position.Y - tolerance;
+                var maxY = text.Position.Y + text.Height + tolerance;
+
+                if (worldPoint.X >= minX && worldPoint.X <= maxX &&
+                    worldPoint.Y >= minY && worldPoint.Y <= maxY)
+                    return text;
+            }
+
+            return null;
+        }
+
+        private void ShowTextContextMenu(CadText text, Point location)
+        {
+            var menu = new ContextMenuStrip();
+            var item = menu.Items.Add($"Convert \"{text.Value}\" to Geometry");
+            item.Click += (s, e) => TextConvertRequested?.Invoke(this, text);
+            menu.Show(this, location);
+        }
+
         private void DrawEntityLabels(Graphics g)
         {
             for (var i = 0; i < Entities.Count; i++)