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/repository/actor.rs

@@ -0,0 +1,34 @@
+use anyhow::Result;
+use async_trait::async_trait;
+
+use super::RemoteActor;
+
+/// Manages local actor keypairs, remote actor cache, and Announce tracking.
+#[async_trait]
+pub trait ActorRepository: Send + Sync {
+    // ── Local keypairs ──────────────────────────────────────────────────────
+    async fn get_local_actor_keypair(
+        &self,
+        user_id: uuid::Uuid,
+    ) -> Result<Option<(String, String)>>;
+    async fn save_local_actor_keypair(
+        &self,
+        user_id: uuid::Uuid,
+        public_key: String,
+        private_key: String,
+    ) -> Result<()>;
+
+    // ── Remote actor cache ──────────────────────────────────────────────────
+    async fn upsert_remote_actor(&self, actor: RemoteActor) -> Result<()>;
+    async fn get_remote_actor(&self, actor_url: &str) -> Result<Option<RemoteActor>>;
+
+    // ── Boost (Announce) tracking ───────────────────────────────────────────
+    async fn add_announce(
+        &self,
+        activity_id: &str,
+        object_url: &str,
+        actor_url: &str,
+        announced_at: chrono::DateTime<chrono::Utc>,
+    ) -> Result<()>;
+    async fn count_announces(&self, object_url: &str) -> Result<usize>;
+}