fix: AP bugs — backfill mapping, review activity type, also_known_as parse

- BackfillRequested now maps to BackfillFollower domain event (not FollowAccepted);
  worker calls run_backfill_for_follower to send LOCAL content to new follower inbox,
  instead of incorrectly trying to import from an inbox URL as if it were an outbox
- reviews broadcast as Create activity instead of Add (semantically correct)
- also_known_as JSON parse failure logs warning + preserves raw string as single-element
  vec instead of silently returning empty

crates/adapters/activitypub/src/port.rs

@@ -34,6 +34,7 @@ pub trait ActivityPubPort: Send + Sync {
     async fn import_remote_outbox(&self, outbox_url: &str, actor_url: &str) -> anyhow::Result<()>;
     async fn followers_collection_json(&self, user_id: Uuid, page: Option<u32>) -> anyhow::Result<String>;
     async fn following_collection_json(&self, user_id: Uuid, page: Option<u32>) -> anyhow::Result<String>;
+    async fn run_backfill_for_follower(&self, owner_user_id: Uuid, follower_inbox_url: String) -> anyhow::Result<()>;
 }
 
 #[async_trait]
@@ -109,6 +110,9 @@ impl ActivityPubPort for ActivityPubService {
     async fn following_collection_json(&self, user_id: Uuid, page: Option<u32>) -> anyhow::Result<String> {
         self.following_collection_json(user_id, page).await
     }
+    async fn run_backfill_for_follower(&self, owner_user_id: Uuid, follower_inbox_url: String) -> anyhow::Result<()> {
+        self.run_backfill_for_follower(owner_user_id, follower_inbox_url).await
+    }
 }
 
 pub struct NoopActivityPubService;
@@ -175,4 +179,7 @@ impl ActivityPubPort for NoopActivityPubService {
     async fn following_collection_json(&self, _: Uuid, _: Option<u32>) -> anyhow::Result<String> {
         Ok(String::new())
     }
+    async fn run_backfill_for_follower(&self, _: Uuid, _: String) -> anyhow::Result<()> {
+        Ok(())
+    }
 }