feat(feed): embed PeerTube videos in the News feed
A federated PeerTube link (/w/<id> or /videos/watch/<id>, any instance) now renders as an inline
player in the feed, next to the YouTube/Spotify/SoundCloud/Vimeo/Bandcamp/Apple embeds. PeerTube is
decentralised, so it's matched by its watch-URL pattern (host validated for safe iframe-src) rather
than a fixed domain, and embeds to <host>/videos/embed/<id>. CSP frame-src 'self' https: already
allows it; added only in the feed builder (not the shared detectProvider).
Co-Authored-By: Claude <noreply@…>