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/port.rs

@@ -31,7 +31,9 @@ pub trait ActivityPubPort: Send + Sync {
     async fn add_blocked_domain(&self, domain: &str, reason: Option<&str>) -> anyhow::Result<()>;
     async fn remove_blocked_domain(&self, domain: &str) -> anyhow::Result<()>;
     async fn get_blocked_domains(&self) -> anyhow::Result<Vec<BlockedDomain>>;
-    async fn backfill_outbox(&self, outbox_url: &str, actor_url: &str) -> anyhow::Result<()>;
+    async fn import_remote_outbox(&self, outbox_url: &str, actor_url: &str) -> anyhow::Result<()>;
+    async fn followers_collection_json(&self, user_id: Uuid, page: Option<u32>) -> anyhow::Result<String>;
+    async fn following_collection_json(&self, user_id: Uuid, page: Option<u32>) -> anyhow::Result<String>;
 }
 
 #[async_trait]
@@ -98,8 +100,14 @@ impl ActivityPubPort for ActivityPubService {
     async fn get_blocked_domains(&self) -> anyhow::Result<Vec<BlockedDomain>> {
         self.get_blocked_domains().await
     }
-    async fn backfill_outbox(&self, outbox_url: &str, actor_url: &str) -> anyhow::Result<()> {
-        self.backfill_outbox(outbox_url, actor_url).await
+    async fn import_remote_outbox(&self, outbox_url: &str, actor_url: &str) -> anyhow::Result<()> {
+        self.import_remote_outbox(outbox_url, actor_url).await
+    }
+    async fn followers_collection_json(&self, user_id: Uuid, page: Option<u32>) -> anyhow::Result<String> {
+        self.followers_collection_json(user_id, page).await
+    }
+    async fn following_collection_json(&self, user_id: Uuid, page: Option<u32>) -> anyhow::Result<String> {
+        self.following_collection_json(user_id, page).await
     }
 }
 
@@ -158,7 +166,13 @@ impl ActivityPubPort for NoopActivityPubService {
     async fn get_blocked_domains(&self) -> anyhow::Result<Vec<BlockedDomain>> {
         Ok(vec![])
     }
-    async fn backfill_outbox(&self, _: &str, _: &str) -> anyhow::Result<()> {
+    async fn import_remote_outbox(&self, _: &str, _: &str) -> anyhow::Result<()> {
         Ok(())
     }
+    async fn followers_collection_json(&self, _: Uuid, _: Option<u32>) -> anyhow::Result<String> {
+        Ok(String::new())
+    }
+    async fn following_collection_json(&self, _: Uuid, _: Option<u32>) -> anyhow::Result<String> {
+        Ok(String::new())
+    }
 }