fix(plex): address code-review findings (F1-F3, F5, F9)

- F1: refresh grid after playback/collection-edit — invalidate the renamed
  ["plex-library"] query key in PlexPlayer + PlexCollectionEditor (was stale
  ["plex-browse"], a dead no-op)
- F2: exclude hidden movies from facet counts/bounds — the movie facet base now
  always joins watch-state and mirrors unified_library's status branches, so
  facets match the visible grid exactly
- F3: show_detail/item_detail live-Plex enrichment degrades instead of 500ing —
  broaden the best-effort block to except Exception
- F5: don't re-run the heavy facet computation on sort-direction toggles — key
  the facets query only on fields plexFacets actually sends
- F9: optimistic watched-toggle also updates the search Episodes section and
  gives toggleEpisodeWatched an optimistic path (shared optimisticStatus helper)

frontend/src/components/PlexCollectionEditor.tsx

@@ -50,7 +50,7 @@ export default function PlexCollectionEditor({
   const refresh = () => {
     qc.invalidateQueries({ queryKey: ["plex-collections"] });
     qc.invalidateQueries({ queryKey: ["plex-item", item.id] });
-    qc.invalidateQueries({ queryKey: ["plex-browse"] });
+    qc.invalidateQueries({ queryKey: ["plex-library"] });
     onChanged();
   };