feat(plex): search cast & crew names + clickable person cards

Backend (migration 0046_plex_people_search): a new people_text column (cast +
director names, de-duped) is folded into the generated search_vector at weight B,
so the top search box finds titles by an actor/director name and ranks them above
summary-only mentions. New /api/plex/people endpoint returns the cast/crew matching
the term (name prefix or word-start) with a film count + a headshot (pulled from one
representative film's live metadata; image bytes disk-cached).

Frontend: PlexBrowse shows matching people as virtual cards above the grid; clicking
one adds them to the actor/director filter (multi-value, from the C1 work) and clears
the search box so you land on exactly that person's films. Answers the 'why does
"drew" match Rambo?' confusion — it was matching the word in the synopsis; now names
are searchable. i18n en/hu/de.

⚠️ Prod needs a Plex re-sync after deploy to populate people_text (search_vector
regenerates automatically once the column has data).

backend/app/models.py

@@ -1044,10 +1044,14 @@ class PlexItem(Base, TimestampMixin, UpdatedAtMixin):
     genres: Mapped[list | None] = mapped_column(JSONB)
     directors: Mapped[list | None] = mapped_column(JSONB)
     cast_names: Mapped[list | None] = mapped_column(JSONB)
+    # Cast + director names, space-joined — folded into search_vector (weight B) so the search box
+    # finds titles by a person's name (and ranks them above summary-only mentions).
+    people_text: Mapped[str | None] = mapped_column(Text)
     search_vector: Mapped[object | None] = mapped_column(
         TSVECTOR,
         Computed(
             "setweight(to_tsvector('public.unaccent_simple', coalesce(title, '')), 'A') || "
+            "setweight(to_tsvector('public.unaccent_simple', coalesce(people_text, '')), 'B') || "
             "setweight(to_tsvector('public.unaccent_simple', left(coalesce(summary, ''), 1000)), 'C')",
             persisted=True,
         ),