fix: implement clone method for DrawingOptions and remove signature mode init

The clone method in DrawingOptions was previously unimplemented, now it properly creates a copy. Also removed unnecessary signature mode initialization in sign-pdf.ts as it's handled elsewhere.

public/pdfjs-viewer/pdf.mjs

@@ -21663,7 +21663,9 @@ class DrawingOptions {
     this.updateProperties(options);
   }
   clone() {
-    unreachable("Not implemented");
+    const copy = new this.constructor();
+    copy.updateAll(this);
+    return copy;
   }
 }
 class DrawingEditor extends AnnotationEditor {

src/js/logic/sign-pdf.ts

@@ -69,15 +69,6 @@ export async function setupSignTool() {
         if (editorStampButton) {
           editorStampButton.disabled = false;
         }
-
-        // Ensure annotation editor is fully enabled; start in Signature mode
-        const pdfViewer = app.pdfViewer;
-        const AnnotationEditorType = viewerWindow.pdfjsLib?.AnnotationEditorType;
-        if (pdfViewer && AnnotationEditorType) {
-          pdfViewer.annotationEditorMode = {
-            mode: AnnotationEditorType.SIGNATURE,
-          };
-        }
       }
     } catch (e) {
       console.error('Could not initialize base PDF.js viewer for signing:', e);