feat(plex): every card rail in the reader's language; an episode in a poster rail stands as its show (E30 S1b)

The grid served Hungarian titles, but every other card surface (Discover rails, the
show page's episodes, search, collections, the person page, playlists, Home's resume
rail, hero and comfort shelf) served English. The card serializers now take a
required keyword-only lang (a forgotten call site fails instead of going English), and
each of those reads takes ?lang=hu, with the language in its query key. A Hungarian
search finds an episode by its Hungarian title too.

An episode on a poster rail showed its 16:9 still cropped into a poster, titled only
with the episode name; it now shows the show's poster and name, with S·E · title under
it (option A). Plex's generic season names (Season 1, Specials) are rebuilt from the
number in the reader's language; a season with a name of its own keeps it.

Home's comfort-shelf move wrote its optimistic order to the key without the language,
which nothing read any more; it writes the query's own key.

backend/app/routes/plex/people.py

@@ -18,7 +18,7 @@ from app.models import (
 )
 from app.plex import rollup
 from app.plex import tmdb as plex_tmdb
-from app.plex.cards import movie_card, show_card
+from app.plex.cards import movie_card, norm_lang, show_card
 from app.plex.query import content_libs, split_csv
 
 router = APIRouter(prefix="/api/plex", tags=["plex"])
@@ -31,6 +31,7 @@ def _resolve_known_for(
     uid: int,
     movie_lib_ids: list[int],
     show_lib_ids: list[int],
+    lang: str,
 ) -> list[dict]:
     """The person's TMDB "Known for" credits (top by popularity) that are IN our library, as cards, in
     popularity order. Matched by the canonical guid `tmdb:<id>`; out-of-library credits are dropped."""
@@ -50,9 +51,9 @@ def _resolve_known_for(
         # A credit resolves against its OWN media_type's bucket only.
         if k.get("media_type") == "tv":
             if g in shows:
-                out.append(show_card(shows[g], show_statuses.get(shows[g].id, "new")))
+                out.append(show_card(shows[g], show_statuses.get(shows[g].id, "new"), lang=lang))
         elif g in movies:
-            out.append(movie_card(movies[g], m_states.get(movies[g].id)))
+            out.append(movie_card(movies[g], m_states.get(movies[g].id), lang=lang))
     return out
 
 
@@ -159,6 +160,7 @@ def _enrich_person_bg(person_id: int) -> None:
 def person_detail(
     name: str,
     background_tasks: BackgroundTasks,
+    lang: str = "en",
     user: User = Depends(current_user),
     db: Session = Depends(get_db),
 ) -> dict:
@@ -173,6 +175,7 @@ def person_detail(
     The fetch runs OFF the request path (a background task); the first open serves whatever's in the row
     (bio possibly still null) and the bio lands from the row by the next open.
     """
+    lang = norm_lang(lang)
     person = db.execute(select(PlexPerson).where(PlexPerson.name == name)).scalars().first()
     # Lazy one-time bio enrich, scheduled AFTER the response so the TMDB call is never on the serve path.
     # Gated by a per-person cooldown so concurrent/rapid opens (or repeated opens while TMDB is degraded)
@@ -206,7 +209,7 @@ def person_detail(
             .all()
         )
         states = rollup.item_state_map(db, user.id, [it.id for it in items])
-        movies = [movie_card(it, states.get(it.id)) for it in items]
+        movies = [movie_card(it, states.get(it.id), lang=lang) for it in items]
 
     shows: list[dict] = []
     if show_lib_ids:
@@ -227,10 +230,10 @@ def person_detail(
             .all()
         )
         statuses = rollup.state_map(db, user.id, [s.id for s in show_rows])
-        shows = [show_card(sh, statuses.get(sh.id, "new")) for sh in show_rows]
+        shows = [show_card(sh, statuses.get(sh.id, "new"), lang=lang) for sh in show_rows]
 
     known_for = _resolve_known_for(
-        db, person.known_for if person else None, user.id, movie_lib_ids, show_lib_ids
+        db, person.known_for if person else None, user.id, movie_lib_ids, show_lib_ids, lang
     )
     return {
         "name": name,