fix(e5): Plex detail/UI polish from review (backdrop reset, layout, combobox, labels)

User-reported issues after the E5 build:

- useCrossfadeBackdrop: the static branch (one image / crossfade off /
  reduced motion) painted #root but returned NO cleanup, so the backdrop
  persisted after leaving the page (e.g. switching modules). Every painted
  branch now returns clear() so unmount always resets the default backdrop.
- scheduler: give the tmdb_enrich job a proper label + description (was the
  raw "tmdb_enrich" id) in EN/HU.
- CastStrip: cap crew names to ONE line (truncate) so the row of circular
  photos sits on one baseline instead of going wavy on 2-line names.
- PlexInfo: lay Details / Keywords / Crew out as side-by-side boxes
  (items-start grid) instead of full-width stacked panels with dead space;
  narrower Crew grid for the boxed width; each panel independently hideable
  from the customize menu (new Details/Keywords/Crew toggles). Tighter
  vertical spacing.
- MultiSelectChips: reshape the trigger from a "+Add" button into an
  Overseerr-style combi input — removable chips inside a typeable field that
  filters the checklist, opening on focus (backspace removes the last chip).
- Discover / person rails: reduce the vertical gap between rails.

frontend/src/components/plexViews.tsx

@@ -144,7 +144,7 @@ export function PlexPersonView({
 
   const section = (titleKey: string, cards: PlexCard[]) =>
     cards.length > 0 ? (
-      <section className="mb-8">
+      <section className="mb-5">
         <h2 className="text-sm font-semibold mb-3">{t(titleKey, { count: cards.length })}</h2>
         <div className="grid grid-cols-[repeat(auto-fill,minmax(150px,1fr))] gap-3">
           {cards.map((c) => (
@@ -237,7 +237,7 @@ export function PlexPersonView({
 
           {/* "Known for" — the person's most-popular titles that are in our library (E5 S6). */}
           {d.known_for.length > 0 && (
-            <section className="mb-8">
+            <section className="mb-5">
               <Carousel title={t("plex.person.knownFor")} ariaLabel={t("plex.person.knownFor")}>
                 {d.known_for.map((c) => (
                   <div key={c.id} className="w-[150px] shrink-0">