refactor(federation): specific AS2 media types (Image/Audio) for attachments, not generic Document
AS2 has dedicated Image/Audio/Video subtypes; we emitted generic Document + mediaType for both
image and audio attachments. Now emit the specific type (derived from mediaType), keeping
mediaType as the interop safety net. More spec-canonical (matches PeerTube/Funkwhale's Video/
Audio); Image/Audio/Video are AS2-core so the shared @context + the AS2 validity test still pass.
- src/services/ActivityPubService.js — attachment type from mediaType (fedi_open audio → Audio, images → Image)
Co-Authored-By: Claude <noreply@…>