ranjithrajv/gitalike ? reverse-engineered prompt

Build me a browser extension that makes GitHub look like GitLab, GitLab look like GitHub, and also supports Bitbucket and self hosted instances like Gitea, Forgejo, Gerrit, and GitHub Enterprise.

I want it to be local only, with no account, no telemetry, no network requests, and nothing sent anywhere. It should change the site’s look and feel, not just the colors, so the words, navigation, reference markers like #42 and !42, and the familiar keyboard shortcuts all match the chosen forge. It should work both ways and undo everything cleanly when I turn it off.

Please make a simple popup where I can choose the skin for the current site, and add a way to register my own site if it is not supported yet. It should feel good in Chrome and Firefox, and work on the major forge sites right away. If you need to look up current browser extension docs online, go ahead.