feat: implement cloud sync

[dolfies]

Settings are synced directly to Discord, no remote server required :)

• Allows picking which account to sync to
• Should work during account switcher use
• Should alert the user if any conflicts happen when saving from multiple clients
• Definitely needs more testing for state bugs

[NotNite]

I just woke up, so I haven't had time to fully review it, but some initial concerns from me:

• We try our best to not show any obvious red flags as a modded client (we aren't perfect, and it's pretty obvious we're modded with something like disableSentry anyways), but I feel a bit uneasy shipping an extension that's by design stuffing extra data in UserSettings no matter how minor. If we shipped this, I think it'd have to be disabled by default and marked with Danger Zone.
• IMO involving moonlight's core config loading with this is the wrong approach; I'd rather have the core extension overwrite the local config on startup, and listen to config saved events to sync it to the server.
• I'm not a big fan of making this a hard dependency of moonbase, but we also don't really have a way to specify a soft dependency right now, so not sure what the best solution is there (another tab in settings, maybe?).

Regardless, the implementation here is really clever, well done! Also, feel free to ignore the Nix CI, I can fix that for you.

[dolfies]

Regarding 1, moonlight is actually already explicitly detected by Discord (and it's not for malicious reasons) so I don't think this makes much of a difference. It's already disabled by default, and I'm not sure how to add a Danger Zone marking given that it's toggled in moonbase, though an extra warning box is probably reasonable

[NotNite]

Regarding 1, moonlight is actually already explicitly detected by Discord (and it's not for malicious reasons) so I don't think this makes much of a difference.

That detection doesn't actually trigger since we don't load libdiscore's separate Webpack entrypoint immediately - I've been meaning to solve it in a more pleasant way in #301.

It's already disabled by default

I'm pretty sure having it as a dependency of Moonbase will enable it, given that we don't have a mechanism to do soft dependency resolution ATM. We should probably fix that... Alternatively, we could not integrate it with Moonbase at all and just have a separate settings tab, I guess?

and I'm not sure how to add a Danger Zone marking given that it's toggled in moonbase

dangerZone tag in the extension manifest.