Person follows are already supported (video_watchlist kind='person', add/remove/check
API, and the button shows on person CARDS) — but the person DETAIL page had no way to
follow or see if a person is followed. Added the standard watchlist button to the
person hero: renderWatchlist() builds it + lazily checks the followed state,
toggleWatch() adds/removes via the person-kind watchlist API, wired through the page's
delegated click handler. Same chrome as the movie/show pages.
4 wiring tests; node --check clean.
