fix(annotation): correctly assign elementId for signature annotations

Previously, signature annotations did not include elementId mapping logic, which caused issues when linking annotations to their corresponding elements. This update adds logic to extract elementId from the nearest signature annotation (similar to frame annotations) to ensure proper association.

EnvelopeGenerator.Web/wwwroot/js/app.js

@@ -250,8 +250,8 @@ class App {
                 // Export annotation data and save to database
                 try {
                     const res = await signEnvelope({
-                        instant: iJSON,
-                        structured: mapSignature(iJSON)
+                        psPfKitInstant: iJSON,
+                        psPfKitStructured: mapSignature(iJSON)
                     });
 
                     if (!res.ok) {