fix(annotations): correctly decode base64 for FRAME annotations

Updated `mapSignature` function to use `fixBase64` when assigning `value`
to FRAME annotations. This ensures any escaped Base64 strings in attachments
are properly converted to standard Base64 format.

EnvelopeGenerator.Web/wwwroot/js/annotation.js

@@ -329,7 +329,7 @@ function mapSignature(iJSON) {
             const idPartsOfPre = preElement.id.split('#');
             annot.elementId = Number(idPartsOfPre[2]);
             annot.name = annot.description.toLowerCase();
-            annot.value = iJSON.attachments[annot.imageAttachmentId]?.binary || null;
+            annot.value = fixBase64(iJSON.attachments[annot.imageAttachmentId]?.binary);
             return annot;
         })
     };