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/application/src/commands.rs

@@ -75,6 +75,7 @@ pub struct DeleteImportProfileCommand {
 
 pub struct UpdateProfileCommand {
     pub user_id: Uuid,
+    pub display_name: Option<String>,
     pub bio: Option<String>,
     pub avatar_bytes: Option<Vec<u8>>,
     pub avatar_content_type: Option<String>,

crates/application/src/use_cases/update_profile.rs

@@ -68,6 +68,7 @@ pub async fn execute(ctx: &AppContext, cmd: UpdateProfileCommand) -> Result<(),
     ctx.user_repository
         .update_profile(
             &user_id,
+            cmd.display_name,
             cmd.bio,
             new_avatar_path,
             new_banner_path,