i18n: add Italian translation

Adds po/it.po covering all 289 source strings, aligned with the current strings in main. Validated with msgfmt -c and msgcmp against a freshly generated POT.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Signed-off-by: Michele <134086208+mikpinky@users.noreply.github.com>

Author: mikpinky