feat(BurnPdfCommandHandler): implement AddInkAnnotation for freehand annotations

- Added implementation for AddInkAnnotation(int page, string value) to render ink annotations from JSON.
- Deserialize ink lines and stroke color, convert points to PDF coordinates, and add as freehand annotations.
- Retained placeholder for AddInkAnnotation(Annotation pAnnotation) for future use.

EnvelopeGenerator.Application/Pdf/BurnPdfCommand.cs

@@ -329,7 +329,23 @@ public class BurnPdfCommandHandler : IRequestHandler<BurnPdfCommand>
 
     private void AddInkAnnotation(int page, string value)
     {
-        throw new NotImplementedException();
+        var ink = JsonConvert.DeserializeObject<Ink>(value);
+
+        var oSegments = ink?.Lines.Points;
+        var oColor = ColorTranslator.FromHtml(ink?.StrokeColor ?? "#000000");
+        _manager.SelectPage(page);
+
+        if (oSegments is null)
+            return;
+
+        foreach (var oSegment in oSegments)
+        {
+            var oPoints = oSegment
+                .Select(ToPointF)
+                .ToArray();
+
+            _manager.AddFreeHandAnnot(oColor, oPoints);
+        }
     }
 
     private void AddInkAnnotation(Annotation pAnnotation)