I created a simple little Jekyll site to host encrypted versions of passwords, and to decrypt all the passwords to plaintext client-side once a password is entered. New passwords can be encrypted client side and added manually to the Jekyll site via committing to the git repo. It's hosted for free on Github pages. Something like Netlify CMS could remove the manual aspect of it by providing an auth+backhaul to update the git repo via a client side gui.

Is this a terrible idea? If so, why?

Demo repo: https://github.com/cameroncowden/passwordman

Demo site: http://ge0de.ninja/