refactor!: CQRS repository split — v0.3.0

FederationRepository (34 methods) → 4 focused traits:
  ActivityRepository  (2)  — idempotency tracking
  FollowRepository    (18) — follower/following graph + migration
  ActorRepository     (6)  — keypairs, remote actor cache, announce tracking
  BlocklistRepository (8)  — domain + actor blocklists

ApObjectHandler (10 methods) → 2 traits:
  ApContentReader  (3) — get_local_objects_for_user/page, count_local_posts
  ApObjectHandler  (9) — all inbox callbacks (on_create, on_mention, etc.)

Builder changes from positional args to named setters:
  ActivityPubService::builder(base_url)
    .activity_repo(arc)
    .follow_repo(arc)
    .actor_repo(arc)
    .blocklist_repo(arc)
    .user_repo(arc)
    .content_reader(arc)
    .object_handler(arc)
    .build()

No behaviour changes.

src/outbox.rs

@@ -66,7 +66,7 @@ pub async fn outbox_handler(
     // if count_local_posts returns 0. In practice this trait method is called
     // infrequently (only on the root collection endpoint).
     let total = data
-        .object_handler
+        .content_reader
         .count_local_posts()
         .await
         .map_err(|e| Error::from(anyhow::anyhow!("{}", e)))?;
@@ -75,7 +75,7 @@ pub async fn outbox_handler(
         let before: Option<DateTime<Utc>> = query.before.as_deref().and_then(|s| s.parse().ok());
 
         let items = data
-            .object_handler
+            .content_reader
             .get_local_objects_page(uuid, before, AP_PAGE_SIZE)
             .await
             .map_err(|e| Error::from(anyhow::anyhow!("{}", e)))?;