Please also note that the link to github from https://kleopatra.app/ is broken and that your repository seems to miss a license. If it is not marked with the right holders and a Free Software license, users cannot see that it is Free Software (sometimes called “Open Source”). (See https://reuse.software for a modern way to mark software source code as Free Software.)
Hope you can do both changes and then get a useful web tool.
BTW I am not sure that OpenPGP.js is fully LibrePGP compatible, which is the modern standard GnuPG is using. Default algorithms would be ECC.
Users will still have to trust the application a lot as the web server can always issue a different version of the software and could issue a version that sends the private key or the cipher text somewhere. You will probably have to address this at some point as well.
Welcome to crypto coding!
Best Regards,
Bernhard
ps.: I have added a “.add” and remove the “[open source]” from your original title to avoid confusion of other readers, I hope that is okay?