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.

frontend/src/i18n/locales/en/plex.json

@@ -63,6 +63,7 @@
   "empty": "Nothing here yet. Run a Plex sync from the admin Config page.",
   "loadMore": "Load more",
   "watched": "Watched",
+  "inProgress": "In progress",
   "play": "Play",
   "resume": "Resume",
   "openShow": "Open show",