i18n: add missing Spanish localization strings

The Spanish localizations have become slightly outdated as the maintainer (@XNovaDelta) seems to have become MIA (?), use `npm run langs:format` to edit the localization files interactively... Anyone is welcome to deal with the missing strings, and if being a maintainer for the Spanish localizations is of your interest, feel free to also edit the `maintainers.json` file: ``` cli.update.failed gui.mods.cant_find_specific gui.mods.cant_find_version gui.browser.sort.newest gui.browser.sort.last_updated gui.browser.sort.highest_rating gui.browser.sort.most_downloads gui.toast.title.failed_to_connect gui.toast.title.missing_steam gui.toast.title.missing_flatpak gui.toast.title.missing_flatpak_steam gui.toast.desc.failed_to_connect gui.toast.desc.failed_launch_command gui.toast.desc.missing_launch_command gui.toast.desc.missing_steam gui.toast.desc.missing_flatpak gui.toast.desc.missing_flatpak_steam viper.already_running tooltip.offline ```