feat(ap): ActivityPub spec compliance and profile completeness

Phase 1 — spec compliance:
- Add AS_PUBLIC constant; add to/cc fields to CreateActivity, DeleteActivity,
  UpdateActivity, AddActivity; populate on all broadcast call sites
- Add @context to outbox CreateActivity items
- Set manuallyApprovesFollowers: true to match actual Pending follow flow
- Gate PermissiveVerifier behind FEDERATION_DEBUG env var
- Add updated timestamp to Person actor JSON
- Improve actor update delivery logging

Phase 2a Batch 1 — AP layer:
- Add /inbox shared inbox route; add endpoints.sharedInbox to Person
- Paginate followers and following collections (20/page, OrderedCollectionPage)

Phase 2a Batch 2 — profile completeness:
- DB migrations: banner_path, also_known_as columns; user_profile_fields table
- ProfileField value object; UserProfileFieldsRepository port
- Banner image upload (stored via image-converter, surfaced as image in Person)
- alsoKnownAs field in Person (account migration support)
- Custom profile fields (up to 4 PropertyValue attachments in Person)
- Profile settings UI: banner preview/upload, alsoKnownAs input, fields form
- PUT /api/v1/profile/fields API endpoint

crates/adapters/activitypub-base/src/repository.rs

@@ -58,6 +58,19 @@ pub trait FederationRepository: Send + Sync {
         remote_actor_url: &str,
     ) -> Result<()>;
     async fn get_followers(&self, local_user_id: uuid::Uuid) -> Result<Vec<Follower>>;
+    async fn get_followers_page(
+        &self,
+        local_user_id: uuid::Uuid,
+        offset: u32,
+        limit: usize,
+    ) -> Result<Vec<Follower>>;
+    async fn count_followers(&self, local_user_id: uuid::Uuid) -> Result<usize>;
+    async fn get_following_page(
+        &self,
+        local_user_id: uuid::Uuid,
+        offset: u32,
+        limit: usize,
+    ) -> Result<Vec<RemoteActor>>;
     async fn update_follower_status(
         &self,
         local_user_id: uuid::Uuid,