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/plex/sync.py

@@ -183,6 +183,9 @@ def _apply_item(row: PlexItem, lib_id: int, kind: str, meta: dict) -> None:
     row.genres = _tags(meta, "Genre")
     row.directors = _tags(meta, "Director")
     row.cast_names = _tags(meta, "Role", limit=20)
+    # Searchable people blob (cast + directors, de-duped) → folded into search_vector at sync time.
+    people = list(dict.fromkeys((row.directors or []) + (row.cast_names or [])))
+    row.people_text = " ".join(people) or None
     mf = _media_facts(meta)
     row.file_path = mf.get("file_path")
     row.part_key = mf.get("part_key")