feat(plex): expanded metadata filters, clickable info page, image disk cache

Backend (migration 0045_plex_filter_meta): plex_items gains rating (audienceRating
~IMDb), content_rating, studio, originally_available_at, and GIN-indexed genres /
directors / cast_names — all mirrored from the cheap section listing (no per-item API
calls; they also seed a future watch-habit recommender). /browse gains genre / content-
rating / year / rating / duration / added-within / director / actor / studio filters
(@> containment, GIN) + sort by year|rating|duration|release; new /facets endpoint
returns available genres+ratings (with counts) and the year/rating/duration bounds. A
thin on-disk image cache (.plex-img-cache) serves posters/art/cast photos from local
disk after first fetch (~7-14x faster repeat loads).

Frontend: PlexSidebar grows the full filter set (facet-driven genre/age chips, rating
steps, year range inputs, duration buckets, added-within, active people/studio chips,
clear-all); filters persist per-account as one JSON blob. PlexInfo metadata (year,
genre, director, cast, studio, IMDb score) is clickable → sets the matching filter and
returns to the filtered grid (page variant only; the in-player overlay stays read-only
so a stray click can't stop playback). i18n en/hu/de.

frontend/src/lib/storage.ts

@@ -26,6 +26,7 @@ export const LS = {
   plexLibrary: "siftlode.plexLibrary",
   plexShow: "siftlode.plexShow",
   plexSort: "siftlode.plexSort",
+  plexFilters: "siftlode.plexFilters",
   notifHistory: "siftlode.notifications",
   notifSettings: "siftlode.notifSettings",
   onboardingDismissed: "siftlode.onboarding.dismissed",