fix(fediverse): expose cover via Note.image for player-card posts (Cirkel covers)
Hosted-audio posts suppress the image attachment so Mastodon shows the player
card; that left the Cirkel/timeline cards coverless. buildNote now also sets the
Note's AS2 image (Mastodon ignores it), and handleInbox uses it as a cover
fallback. scripts/backfill-cirkel-covers.mjs re-fetches existing coverless
timeline notes to fill them in.
Co-Authored-By: Claude <noreply@…>