feat(fediverse): NodeInfo 2.1 + per-note replies collection
NodeInfo (/.well-known/nodeinfo + /nodeinfo/2.1) so fediverse tools recognise the
instance (software 'klonkt', user/post counts). Notes now carry a 'replies'
OrderedCollection (/ap/notes/:id/replies) listing inbound + our own reply note
URIs, so remote servers can fetch the whole thread.
Co-Authored-By: Claude <noreply@…>