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/domain/src/models/mod.rs

@@ -461,6 +461,8 @@ impl FeedEntry {
 pub struct UserSummary {
     pub user_id: UserId,
     email: Email,
+    username: Username,
+    display_name: Option<String>,
     pub total_movies: i64,
     pub avg_rating: Option<f64>,
     pub avatar_path: Option<String>,
@@ -470,6 +472,8 @@ impl UserSummary {
     pub fn new(
         user_id: UserId,
         email: Email,
+        username: Username,
+        display_name: Option<String>,
         total_movies: i64,
         avg_rating: Option<f64>,
         avatar_path: Option<String>,
@@ -477,6 +481,8 @@ impl UserSummary {
         Self {
             user_id,
             email,
+            username,
+            display_name,
             total_movies,
             avg_rating,
             avatar_path,
@@ -485,6 +491,12 @@ impl UserSummary {
     pub fn email(&self) -> &str {
         self.email.value()
     }
+    pub fn username(&self) -> &str {
+        self.username.value()
+    }
+    pub fn display_name(&self) -> Option<&str> {
+        self.display_name.as_deref()
+    }
 }
 
 #[derive(Clone, Debug)]