chore: prevent user selection within signature pad (documenso#1530)

adds a `select-none` class to the signature pad in order to
prevent iPadOS from becoming too trigger happy with the context menu and
auto corrects. Please ensure this doesn't break anything by accident.

packages/ui/primitives/signature-pad/signature-pad.tsx

@@ -461,7 +461,7 @@ export const SignaturePad = ({
 
   return (
     <div
-      className={cn('relative block', containerClassName, {
+      className={cn('relative block select-none', containerClassName, {
         'pointer-events-none opacity-50': disabled,
       })}
     >