SocialQuery returns SocialActor (identity+handle+display_name+avatar_url)
instead of bare SocialIdentity. Migrated get_following_page,
get_followers_page, get_blocked_actors_page to use cases. Moved
get_activity_feed + get_profile from SocialQueryPort to SocialQuery.
Legacy SocialQueryPort remains only for get_users listing.
SocialIdentity value object (Local|Remote), SocialCommand/SocialQuery
domain ports, 11 CQRS use cases w/ 14 tests, CompositeSocialAdapter
wrapping k_ap, 6 new domain events, handlers migrated from ap_service
to use cases. Closes#12 foundation — AP handlers + legacy cleanup TBD.
