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/discover/queries.py

@@ -40,7 +40,7 @@ from app.models import (
     VideoState,
 )
 from app.plex import rollup
-from app.plex.cards import leaf_card, movie_card, show_card
+from app.plex.cards import display_title, leaf_card, movie_card, show_card
 from app.plex.query import apply_show_state_filter, content_libs
 
 # How many rows a single rail may carry — Home's rails and the Plex module's Discover rails alike
@@ -221,7 +221,9 @@ def _unseen_movie_conds(uid: int):
     return ~seen
 
 
-def plex_in_progress(db: Session, uid: int, limit: int = RAIL_LIMIT) -> list[tuple[object, dict]]:
+def plex_in_progress(
+    db: Session, uid: int, limit: int = RAIL_LIMIT, *, lang: str
+) -> list[tuple[object, dict]]:
     """In-progress movies + partially-watched shows as (progressed_at, card).
 
     Mirrors `routes/plex/discover.py::_continue_watching` — same `PlexState` predicate for movies (a
@@ -249,7 +251,7 @@ def plex_in_progress(db: Session, uid: int, limit: int = RAIL_LIMIT) -> list[tup
             .limit(limit)
         )
         for it, st in db.execute(mq).all():
-            out.append((st.progress_updated_at, movie_card(it, st)))
+            out.append((st.progress_updated_at, movie_card(it, st, lang=lang)))
 
     if show_libs:
         prog = rollup.agg_subquery(db, uid, include_resumed=True).subquery()
@@ -263,12 +265,14 @@ def plex_in_progress(db: Session, uid: int, limit: int = RAIL_LIMIT) -> list[tup
         for sh, resumed_at in db.execute(
             sq.order_by(prog.c.resumed_at.desc().nullslast()).limit(limit)
         ).all():
-            out.append((resumed_at, show_card(sh, "in_progress")))
+            out.append((resumed_at, show_card(sh, "in_progress", lang=lang)))
 
     return out
 
 
-def plex_surprise(db: Session, uid: int, budget: str, seed: int, limit: int) -> list[dict]:
+def plex_surprise(
+    db: Session, uid: int, budget: str, seed: int, limit: int, *, lang: str
+) -> list[dict]:
     """Unseen playable movies inside the budget, in seeded-shuffle order.
 
     Movies only. A show is not a thing you can start playing, and resolving every candidate show to
@@ -300,14 +304,14 @@ def plex_surprise(db: Session, uid: int, budget: str, seed: int, limit: int) ->
         q = q.where(PlexItem.duration_s <= hi)
     items = db.execute(q).scalars().all()
     states = rollup.item_state_map(db, uid, [it.id for it in items])
-    return [movie_card(it, states.get(it.id)) for it in items]
+    return [movie_card(it, states.get(it.id), lang=lang) for it in items]
 
 
 # Watch states that take an episode out of the running for "what would play next".
 _DONE = ("watched", "hidden")
 
 
-def next_episode(db: Session, uid: int, show_id: int) -> dict | None:
+def next_episode(db: Session, uid: int, show_id: int, *, lang: str) -> dict | None:
     """What "put that show on" means: the episode in progress, else the first unwatched one, else the
     first — over the same `(season, episode)` broadcast ordering `detail.py::_episode_nav` uses.
 
@@ -357,5 +361,9 @@ def next_episode(db: Session, uid: int, show_id: int) -> dict | None:
     ep, st = pick
     show = db.get(PlexShow, show_id)
     return leaf_card(
-        ep, st, show_title=show.title if show else None, show_rk=show.rating_key if show else None
+        ep,
+        st,
+        show_title=display_title(show, lang) if show else None,
+        show_rk=show.rating_key if show else None,
+        lang=lang,
     )