[Feature Suggestion] Streamline UI/Remove Old UI

[Casuallynoted]

One of the things that's bothered me about Pixelfed for a while is that while it switched to a new UI a few years ago, the old UI is still very much there and is required for a few things still/the button to go to the old UI is always there. I'm not sure if it's within the scope of this project, but I've lowkey been wanting to see all old UI elements get scrubbed in favor of a unified interface.

[Murazaki]

As you may have already done, I checked the UI code, and we can clearly see that a Vue translation is being made but has not been finished. Old UI files that have been ported are still there too.

Furthermore, I've ran some performance tests, and Pixelfed is clearly one of the slowest to render of the ActivityPub space. One would argue it is because of the content shared, but in reality, javascript code and interface assets caching issues are mostly to blame. There's a lot of work to be done on that front too.