feat: migrate k-ap 0.1.10→0.3.1, fix AP gaps

- split FederationRepository into FollowRepository, ActorRepository, BlocklistRepository, ActivityRepository
- RemoteActor: 5 new fields (bio, banner_url, followers_url, following_url, also_known_as)
- ApObjectHandler split: get_local_objects_page/count_local_posts → ApContentReader trait
- builder API: positional args → named setters
- broadcast_create_note/update_note: add ApVisibility + mentioned_inboxes params
- backfill_outbox → import_remote_outbox
- ApUser: also_known_as Option<String> → Vec<String>, new fields

AP gaps fixed:
- add GET /users/{id}/followers + /following with content negotiation
- wire EventPublisher into builder via FederationEventBridge adapter
- add display_name field full stack (domain→DB→API→AP)
- DB-side outbox pagination (get_local_reviews_page)
- set featured_url on ApUser

crates/worker/src/follow_backfill_handler.rs

@@ -20,7 +20,7 @@ impl EventHandler for FollowBackfillHandler {
         };
         tracing::info!(actor = %remote_actor_url, outbox = %outbox_url, "starting outbox backfill");
         self.ap_service
-            .backfill_outbox(outbox_url, remote_actor_url)
+            .import_remote_outbox(outbox_url, remote_actor_url)
             .await
             .map_err(|e| DomainError::InfrastructureError(e.to_string()))
     }