YePpHa/YouTubeCenter ? reverse-engineered prompt

Build me a browser add on for YouTube that makes watching videos more useful again.

I want it to add a small control panel on YouTube pages where I can quickly download the video I’m watching, pick my preferred video quality automatically, and turn on a few helpful extras that make the site easier to use. It should feel like a normal YouTube upgrade, not something flashy or distracting.

Please make it work as a userscript or browser extension that can be built and packaged cleanly, and keep the settings simple enough that a regular person could understand them. If parts of YouTube have changed, update the logic so it still works on the current site as best as possible, and look up current docs online if you need to. Also include a basic way to manage language strings and keep the interface tidy.