Korean (ko): Catch-up with EN version

[henrif75]

Translate remaining messages and review fuzzy translations. As of 6/5/24, current translation stats are:

ko.po
2646 translated messages, 619 fuzzy translations, 508 untranslated messages.

Steps:

1. Sync your branch with main.
2. Recreate messages.pot:

MDBOOK_OUTPUT='{"xgettext": {"pot-file": "messages.pot", "granularity": 0}}' \
  mdbook build -d po

3. Merge with the ko.po:

msgmerge --update po/ko.po po/messages.pot

4. Edit the ko.po file with your favorite PO editor.