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/postgres/migrations/0020_kap_v03.sql

@@ -0,0 +1,12 @@
+-- k-ap 0.3: new RemoteActor fields + activity dedup table
+
+ALTER TABLE ap_remote_actors ADD COLUMN IF NOT EXISTS bio TEXT;
+ALTER TABLE ap_remote_actors ADD COLUMN IF NOT EXISTS banner_url TEXT;
+ALTER TABLE ap_remote_actors ADD COLUMN IF NOT EXISTS followers_url TEXT;
+ALTER TABLE ap_remote_actors ADD COLUMN IF NOT EXISTS following_url TEXT;
+ALTER TABLE ap_remote_actors ADD COLUMN IF NOT EXISTS also_known_as TEXT; -- JSON array
+
+CREATE TABLE IF NOT EXISTS ap_activities (
+    id TEXT PRIMARY KEY,
+    processed_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);