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/sqlite/src/models.rs

@@ -7,7 +7,7 @@ use domain::{
     },
     value_objects::{
         Comment, Email, ExternalMetadataId, MovieId, MovieTitle, PosterPath, Rating, ReleaseYear,
-        ReviewId, UserId, WatchlistEntryId,
+        ReviewId, UserId, Username, WatchlistEntryId,
     },
 };
 use uuid::Uuid;
@@ -245,6 +245,8 @@ impl FeedRow {
 pub(crate) struct UserSummaryRow {
     pub id: String,
     pub email: String,
+    pub username: String,
+    pub display_name: Option<String>,
     pub total_movies: i64,
     pub avg_rating: Option<f64>,
     pub avatar_path: Option<String>,
@@ -255,6 +257,8 @@ impl UserSummaryRow {
         Ok(UserSummary::new(
             UserId::from_uuid(parse_uuid(&self.id)?),
             Email::new(self.email)?,
+            Username::new(self.username)?,
+            self.display_name,
             self.total_movies,
             self.avg_rating,
             self.avatar_path,