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/postgres-federation/src/lib.rs

@@ -58,7 +58,12 @@ fn pg_remote_actor(row: &sqlx::postgres::PgRow, url_col: &str) -> RemoteActor {
             .try_get::<Option<String>, _>("also_known_as")
             .ok()
             .flatten()
-            .map(|s| serde_json::from_str(&s).unwrap_or_default())
+            .map(|s| {
+                serde_json::from_str::<Vec<String>>(&s).unwrap_or_else(|e| {
+                    tracing::warn!(raw = %s, error = %e, "failed to parse also_known_as JSON");
+                    vec![s]
+                })
+            })
             .unwrap_or_default(),
     }
 }