feat(plex): TV-show metadata sync + series filters (Phase 1 of series view)

Give TV shows the same filterable metadata as movies so the TV grid can be
filtered/sorted, not just library+sort. Backend: migration 0052 adds
rating/content_rating/studio/originally_available_at/genres/directors/cast_names/
people_text to plex_shows (+ GIN/indexes, people_text folded into search_vector);
_sync_shows populates them cheaply from the show section listing (no per-item
calls). /browse show-branch gains the movie filter set (minus duration) plus an
aggregate per-user watch-state (a show rolls up its episodes: all watched=watched,
any progress=in_progress, none=new) with year/rating/release sorts; /facets returns
show facets. Frontend: PlexSidebar renders the metadata filters + watch-state for TV
libraries (duration stays movie-only); show cards show a watched/in-progress badge.
i18n plex.inProgress (en/hu/de). Needs a Plex re-sync to populate the new columns.

backend/app/plex/sync.py

@@ -230,6 +230,16 @@ def _sync_shows(db: Session, plex: PlexClient, lib: PlexLibrary, stats: dict) ->
         sh.art_key = meta.get("art")
         sh.child_count = meta.get("childCount")
         sh.added_at = _epoch(meta.get("addedAt"))
+        # Filterable / orderable metadata — same cheap section-listing tags as movies.
+        sh.rating = _rating(meta)
+        sh.content_rating = (meta.get("contentRating") or None)
+        sh.studio = (meta.get("studio") or None) and str(meta.get("studio"))[:255]
+        sh.originally_available_at = _date(meta.get("originallyAvailableAt"))
+        sh.genres = _tags(meta, "Genre")
+        sh.directors = _tags(meta, "Director")
+        sh.cast_names = _tags(meta, "Role", limit=20)
+        people = list(dict.fromkeys((sh.directors or []) + (sh.cast_names or [])))
+        sh.people_text = " ".join(people) or None
         stats["shows"] += 1
     db.flush()
     show_id = {rk: sh.id for rk, sh in shows.items()}