* feat(i18n): add Korean (ko-kr) translation
Add full Korean (ko-kr) locale for the app UI, translated from the
English (en-us) source with full key parity (746/746 keys) and all
placeholders preserved. Registers the new locale in languages.json
and src/lang/index.ts, mirroring how existing locales are wired up.
* feat(i18n): add Korean tray menu strings to tray.ts
Add ko-kr entry to the tray module's messages map, matching the
existing en-us/zh-cn/zh-tw pattern with full key parity (19/19 keys):
play/pause, next/prev song, collect/uncollect, show/hide main window,
show/hide/lock/unlock/top desktop lyric window, statusbar lyric
toggle, exit, and tooltip labels.
Addresses reviewer feedback on PR #2902.
