- A message with no image or video attachment is chat: extract_media returns
nothing for it, so nothing downloads and no post record is written. A
message that passes keeps every file, numbered as gallery-dl numbers them.
- `discord_authors` in a source's config limits the walk to those posters
(id, username or display name); the edit dialog has a field for it and no
longer drops config keys it has no field for.
- source.display_name (migration 0115), refreshed by every Discord walk, shows
on Subscriptions in place of the two-id URL; a Discord post card names its
channel from the record's `channel`.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
