Terminology improvements

Several terms have been renamed throughout the interface to be clearer and easier to translate.

• Superseded replaces "outdated." When a poll is closed and a newer poll on the same topic replaces it, the old poll is now marked "superseded" rather than "outdated." The new term is more precise: "superseded" means "replaced by a newer version," while "outdated" incorrectly implied the decision was no longer valid.
• Position change theshold. If you change your vote more than 15 minutes after your last save, the system records it as a new stance rather than an edit. This makes it clear when someone has had a significant change of mind, visible in the vote history.