feat(federation): link-only tracks federate their external links (Mastodon cards the player)
A track that's link-only (external Spotify/YouTube/SoundCloud, no hosted file) used to
federate as a "listen on <site>" link + the cover. Now it emits the track's external link(s) in
the note and drops the cover, so Mastodon cards the first (Spotify -> its player) and shows the
rest as clickable links — the fediverse-native version of the on-site track card. Hosted/playable
tracks (own player card) and posts without an external track are unchanged; Klonkt's on-site card
is unchanged.
- src/services/ActivityPubService.js — buildNote collects link-only track external links, suppresses cover, emits links
Co-Authored-By: Claude <noreply@…>