fix: wire DeliveryRequested federation events — outbound AP delivery was broken

FederationEventBridge silently dropped DeliveryRequested events from k-ap,
so no Create/Delete/Accept activities were pushed to follower inboxes.
Reviews only reached remote instances via outbox backfill (pull), and
deletes never propagated.

Bridge now publishes FederationDeliveryRequested domain events through the
event bus; worker calls ap_service.deliver_to_inbox() to send them.

crates/domain/src/events.rs

@@ -65,6 +65,11 @@ pub enum DomainEvent {
         owner_user_id: UserId,
         follower_inbox_url: String,
     },
+    FederationDeliveryRequested {
+        inbox_url: String,
+        activity_json: String,
+        signing_actor_id: uuid::Uuid,
+    },
 }
 
 #[async_trait]