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/movies/mod.rs

@@ -1,10 +1,13 @@
 pub mod commands;
 pub mod discovery_indexer;
 pub mod enrich_movie;
+pub mod get_movie_profile;
 pub mod get_movies;
 pub mod queries;
+pub mod reindex_search;
 pub mod search_cleanup;
 pub mod sync_poster;
 
 pub use discovery_indexer::MovieDiscoveryIndexer;
+pub use reindex_search::SearchReindexHandler;
 pub use search_cleanup::SearchCleanupHandler;