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/event-payload/src/lib.rs

@@ -63,6 +63,10 @@ pub enum EventPayload {
         remote_actor_url: String,
         outbox_url: String,
     },
+    BackfillFollower {
+        owner_user_id: String,
+        follower_inbox_url: String,
+    },
 }
 
 impl EventPayload {
@@ -79,6 +83,7 @@ impl EventPayload {
             EventPayload::WatchlistEntryAdded { .. } => "WatchlistEntryAdded",
             EventPayload::WatchlistEntryRemoved { .. } => "WatchlistEntryRemoved",
             EventPayload::FollowAccepted { .. } => "FollowAccepted",
+            EventPayload::BackfillFollower { .. } => "BackfillFollower",
         }
     }
 }
@@ -181,6 +186,13 @@ impl From<&DomainEvent> for EventPayload {
                 remote_actor_url: remote_actor_url.clone(),
                 outbox_url: outbox_url.clone(),
             },
+            DomainEvent::BackfillFollower {
+                owner_user_id,
+                follower_inbox_url,
+            } => EventPayload::BackfillFollower {
+                owner_user_id: owner_user_id.value().to_string(),
+                follower_inbox_url: follower_inbox_url.clone(),
+            },
         }
     }
 }
@@ -281,6 +293,13 @@ impl TryFrom<EventPayload> for DomainEvent {
                 remote_actor_url,
                 outbox_url,
             }),
+            EventPayload::BackfillFollower {
+                owner_user_id,
+                follower_inbox_url,
+            } => Ok(DomainEvent::BackfillFollower {
+                owner_user_id: UserId::from_uuid(parse_uuid(&owner_user_id, "owner_user_id")?),
+                follower_inbox_url,
+            }),
         }
     }
 }