Merge "dark theme" and "night mode"

dark theme (12, but I would say 3 are mis-tagged) <-> night mode (4)
There’s also dark mode (0)

I’m not sure what to recommend as the alias target, but I suggest against dark theme because that’s ambiguous whether it means “low-brightness user interface” or “somber/grim atmosphere or subject matter”

Unfortunately, light theme (3) appears to be the counterpart, whereas light mode (5) has something to do with Jojo’s Bizarre Adventure?

Done.