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/worker/src/follow_backfill_handler.rs

@@ -10,18 +10,29 @@ pub struct FollowBackfillHandler {
 #[async_trait]
 impl EventHandler for FollowBackfillHandler {
     async fn handle(&self, event: &DomainEvent) -> Result<(), DomainError> {
-        let DomainEvent::FollowAccepted {
-            remote_actor_url,
-            outbox_url,
-            ..
-        } = event
-        else {
-            return Ok(());
-        };
-        tracing::info!(actor = %remote_actor_url, outbox = %outbox_url, "starting outbox backfill");
-        self.ap_service
-            .import_remote_outbox(outbox_url, remote_actor_url)
-            .await
-            .map_err(|e| DomainError::InfrastructureError(e.to_string()))
+        match event {
+            DomainEvent::FollowAccepted {
+                remote_actor_url,
+                outbox_url,
+                ..
+            } => {
+                tracing::info!(actor = %remote_actor_url, outbox = %outbox_url, "importing remote outbox");
+                self.ap_service
+                    .import_remote_outbox(outbox_url, remote_actor_url)
+                    .await
+                    .map_err(|e| DomainError::InfrastructureError(e.to_string()))
+            }
+            DomainEvent::BackfillFollower {
+                owner_user_id,
+                follower_inbox_url,
+            } => {
+                tracing::info!(owner = %owner_user_id.value(), inbox = %follower_inbox_url, "backfilling local content to new follower");
+                self.ap_service
+                    .run_backfill_for_follower(owner_user_id.value(), follower_inbox_url.clone())
+                    .await
+                    .map_err(|e| DomainError::InfrastructureError(e.to_string()))
+            }
+            _ => Ok(()),
+        }
     }
 }