feat: search reindex, worker improvements, person IDs, user display names

- add admin POST /api/v1/admin/reindex-search endpoint + event-driven handler
- backfill persons from movie_cast/movie_crew into persons table
- paginate person list_page/backfill_from_credits_batch to cap memory
- concurrent worker event dispatch with semaphore (max 8)
- graceful worker shutdown (drain in-flight tasks on SIGINT)
- always ack events, log handler errors as warnings (no infinite retry)
- NATS ack_wait 600s, AtomicBool guard against concurrent reindex
- add username/display_name to UserSummaryDto and users list
- add person_id to CastMemberDto/CrewMemberDto via get_movie_profile use case
- add movie_id to wrapup MovieRef, person_id to wrapup PersonStat
- thread tmdb_person_id through wrapup cast pipeline
- add is_federated to FeedEntryDto
- cap orphaned persons query with LIMIT 500
- add SPA link to classic site footer

crates/adapters/event-payload/src/lib.rs

@@ -86,6 +86,7 @@ pub enum EventPayload {
     WrapUpCompleted {
         wrapup_id: String,
     },
+    SearchReindexRequested,
 }
 
 impl EventPayload {
@@ -107,6 +108,7 @@ impl EventPayload {
             EventPayload::WatchEventIngested { .. } => "WatchEventIngested",
             EventPayload::WrapUpRequested { .. } => "WrapUpRequested",
             EventPayload::WrapUpCompleted { .. } => "WrapUpCompleted",
+            EventPayload::SearchReindexRequested => "SearchReindexRequested",
         }
     }
 }
@@ -248,6 +250,7 @@ impl From<&DomainEvent> for EventPayload {
             DomainEvent::WrapUpCompleted { wrapup_id } => EventPayload::WrapUpCompleted {
                 wrapup_id: wrapup_id.value().to_string(),
             },
+            DomainEvent::SearchReindexRequested => EventPayload::SearchReindexRequested,
         }
     }
 }
@@ -398,6 +401,7 @@ impl TryFrom<EventPayload> for DomainEvent {
                     wrapup_id: WrapUpId::from_uuid(wid),
                 })
             }
+            EventPayload::SearchReindexRequested => Ok(DomainEvent::SearchReindexRequested),
         }
     }
 }