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/domain/src/models/mod.rs

@@ -321,6 +321,7 @@ pub struct User {
     username: Username,
     password_hash: PasswordHash,
     role: UserRole,
+    display_name: Option<String>,
     bio: Option<String>,
     avatar_path: Option<String>,
     banner_path: Option<String>,
@@ -341,6 +342,7 @@ impl User {
             username,
             password_hash,
             role,
+            display_name: None,
             bio: None,
             avatar_path: None,
             banner_path: None,
@@ -355,6 +357,7 @@ impl User {
         username: Username,
         password_hash: PasswordHash,
         role: UserRole,
+        display_name: Option<String>,
         bio: Option<String>,
         avatar_path: Option<String>,
         banner_path: Option<String>,
@@ -367,6 +370,7 @@ impl User {
             username,
             password_hash,
             role,
+            display_name,
             bio,
             avatar_path,
             banner_path,
@@ -381,11 +385,13 @@ impl User {
 
     pub fn update_profile(
         &mut self,
+        display_name: Option<String>,
         bio: Option<String>,
         avatar_path: Option<String>,
         banner_path: Option<String>,
         also_known_as: Option<String>,
     ) {
+        self.display_name = display_name;
         self.bio = bio;
         self.avatar_path = avatar_path;
         self.banner_path = banner_path;
@@ -407,6 +413,9 @@ impl User {
     pub fn role(&self) -> &UserRole {
         &self.role
     }
+    pub fn display_name(&self) -> Option<&str> {
+        self.display_name.as_deref()
+    }
     pub fn bio(&self) -> Option<&str> {
         self.bio.as_deref()
     }