Add auto-update check

[mccoyweb]

No description provided.

[phenaproxima]

For extra help with debugging, let's also set up logging, as described in https://www.electron.build/auto-update#debugging.

[phenaproxima]

I have a feeling that portable apps on Windows (i.e., what we're building currently) are not auto-updatable. Nowhere does the documentation actually, like, say this...but the fact that latest.yml is not being generated strongly suggests that it's not. Let's switch to a non-portable Windows package by default -- in theory, all we should need to do is remove the target: portable line (and the comment above it) from the win section of electron-builder.yml.

I'll try that in main and see what happens.

EDIT: Confirmed that portable apps don't support auto-updates. I've changed the build target to the default NSIS installer (cd25705) and tested it manually; seems to work pretty well, honestly.

So, as far as I can tell, this is ready to go once we've added the debugging stuff and moved a bit of code around.

Feedback addressed.

[phenaproxima]

Merged in f7dca4d.