Add a promise-based ConfirmProvider + useConfirm() hook (built on the Modal shell,
liquid-glass styling, danger variant, Esc/backdrop = cancel, Enter = confirm) so
confirmations match the app instead of the native browser dialog. Wire it in at the
app root and replace both window.confirm call sites (playlist delete, channel
unsubscribe). Trilingual common.confirm/confirmTitle strings.
Login screen (with a language picker), header, account menu, sync status, About and
Release Notes dialogs, and the version banner are now fully translated in Hungarian,
English and German.
