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/adapters/activitypub/src/federation_event_bridge.rs

@@ -0,0 +1,45 @@
+use std::sync::Arc;
+
+use domain::events::DomainEvent;
+use domain::value_objects::UserId;
+use k_ap::FederationEvent;
+
+pub struct FederationEventBridge {
+    domain_publisher: Arc<dyn domain::ports::EventPublisher>,
+}
+
+impl FederationEventBridge {
+    pub fn new(domain_publisher: Arc<dyn domain::ports::EventPublisher>) -> Self {
+        Self { domain_publisher }
+    }
+}
+
+#[async_trait::async_trait]
+impl k_ap::EventPublisher for FederationEventBridge {
+    async fn publish(&self, event: FederationEvent) -> anyhow::Result<()> {
+        match event {
+            FederationEvent::BackfillRequested {
+                owner_user_id,
+                follower_inbox_url,
+            } => {
+                tracing::info!(
+                    owner = %owner_user_id,
+                    inbox = %follower_inbox_url,
+                    "federation BackfillRequested → FollowAccepted"
+                );
+                self.domain_publisher
+                    .publish(&DomainEvent::FollowAccepted {
+                        local_user_id: UserId::from_uuid(owner_user_id),
+                        remote_actor_url: follower_inbox_url.clone(),
+                        outbox_url: follower_inbox_url,
+                    })
+                    .await
+                    .map_err(|e| anyhow::anyhow!(e.to_string()))
+            }
+            _ => {
+                tracing::debug!("ignoring federation event: {:?}", event);
+                Ok(())
+            }
+        }
+    }
+}