Add READ_AND_CONFIRM JS constant from ViewData flag

Introduced a READ_AND_CONFIRM JavaScript constant in _Layout.cshtml, which reflects the server-side ViewData["ReadAndConfirm"] boolean value. This enables client-side scripts to easily check if the "ReadAndConfirm" flag is set.

EnvelopeGenerator.Web/Views/Shared/_Layout.cshtml

@@ -42,6 +42,8 @@
         const IS_DESKTOP_SIZE = DEVICE_SCREEN_TYPE == 'desktop'
 
         const IS_MOBILE_DEVICE = /Mobi|Android/i.test(window.navigator.userAgent);
+
+        const READ_AND_CONFIRM = @((ViewData["ReadAndConfirm"] is bool readAndConfirm && readAndConfirm).ToString().ToLower())
     </script>
     
     <script src="~/lib/jquery/dist/jquery.min.js"></script>