`kitten themes` treats every .conf in <config-dir>/themes as a user
theme, which the mode system's canonical store was sitting in -- so the
picker was offering three bogus entries named light, dark and
no-preference, and had been since that store was introduced.
Move the store to ./theme-modes so ./themes means only what the kitten
means by it, and repoint apply-theme-mode.sh, the kitten shim, the
run_after hook and the test at the new path.
GrokNight and GrokDay move into ./themes with the ## name/author/
license/upstream/blurb header the kitten reads, so they now show up in
`kitten themes` and `--dump-theme` resolves them.
theme-modes/dark.conf carries the #202020 theme that was already on
disk: the file had to be re-added at its new path, so that drift comes
along with it.
