Refactoring to remove jank workarounds upon sv6 release

[nbitzz]

Lots of things in this codebase can be refactored to take advantage of planned Svelte 6 features like async SSR and remote functions. Use this issue to make note of them, I suppose.

[nbitzz]

Off the top of my head:

• At the time of writing, async SSR doesn't exist yet, so we'll need to pass song data through our page data when writing the song API. We can simplify this with both async SSR & remote functions.
• Remote functions can be used in place of the /net/api workaround-things.