feat(annotation): enhance mapSignature to support drawn signatures

- Added support for mapping drawn (non-image) signatures by including `lines` and `strokeColor` data.
- Added error handling for incompatible or missing signature data structures.
- Ensures compatibility with third-party annotation libraries that return vector-based signatures.

EnvelopeGenerator.Web/wwwroot/js/annotation.js

@@ -335,6 +335,13 @@ function mapSignature(iJSON) {
         signatures: iJSON.annotations.filter(annot => annot.isSignature).map(annot => {
             if (annot.imageAttachmentId)
                 annot.value = iJSON.attachments[annot.imageAttachmentId]?.binary;
+            else if (annot.lines && annot.strokeColor)
+                annot.value = JSON.stringify({
+                    lines: annot.lines,
+                    strokeColor: annot.strokeColor
+                });
+            else
+                throw new Error("Signature mapping failed: The data structure from the third-party library is incompatible or missing required fields.");
 
             annot.name = 'signature';
             return annot;