Sign-up watchlist

Names for the signup-watchlist-alert workflow to match new Nous sign-ups against (exact + close-variant matching, Slack alert per match) — check the workflow is enabled before relying on it. There is no edit — delete and re-add to correct an entry (the re-added entry re-alerts on recent sign-ups, so a fixed typo isn't missed). Email and phone are optional exact-match fields; phone must be E.164 (+44…).