i18n: Add Irish (ga_IE) translation

[aindriu80]

This PR introduces support for Irish (Gaeilge), the first official language of Ireland and an EU working language.

The translation file was initialized using the standard gettext tooling:

msginit -i po/com.mitchellh.ghostty.pot -l $LANG -o "po/$LANG.po"

The locale code ga_IE follows ISO standards for Gaeilge as spoken in Ireland.

I'm happy to volunteer as the ongoing maintainer of the Irish translation and will keep it up to date as Ghostty evolves.

Go raibh maith agat!