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/adapters/nats/src/subject.rs

@@ -14,6 +14,7 @@ pub fn event_to_subject(prefix: &str, event: &DomainEvent) -> String {
         DomainEvent::WatchlistEntryRemoved { .. } => "watchlist.entry.removed",
         DomainEvent::FollowAccepted { .. } => "follow.accepted",
         DomainEvent::BackfillFollower { .. } => "backfill.follower",
+        DomainEvent::FederationDeliveryRequested { .. } => "federation.delivery.requested",
     };
     format!("{prefix}.{suffix}")
 }