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/application/src/wrapup/tests/compute.rs

@@ -26,7 +26,7 @@ fn make_row(title: &str, rating: u8, watched_at: &str) -> WrapUpMovieRow {
         original_language: Some("en".to_string()),
         genres: vec!["Action".to_string()],
         keywords: vec!["heist".to_string()],
-        cast_names: vec![("Actor A".to_string(), 1)],
+        cast_names: vec![("Actor A".to_string(), 1, 12345)],
         cast_profile_paths: vec![None],
     }
 }