fix(plex): resolve deep-review findings on the filter-bar overhaul

Self-review of the branch diff (feature/plex-filter-bar-overhaul) against main:

- Surprise rail query key omitted `lang` while the backend /surprise now filters
  against the language-specific genre column → a HU/EN switch under an active genre
  filter left the rail stale. Key it by scope+lang+filters, matching plexDiscover.
- Chip-removing a collection left its entry in `collectionTitles` (hashed into the
  plex query keys), splitting the cache from the pristine no-collection state and
  growing the titles map unboundedly. Prune the title on remove, like CollectionPicker.
- The saved-views default-mirror effect gained `cfg` in its deps (re-memoized on every
  live filter edit) → a synchronous localStorage write per keystroke. Depend on the
  module-stable mirror fn instead.
- Collections-browse search input had no accessible name (placeholder only). Add
  aria-label + type="search".
- Extract the tile hue-hash + gradient duplicated between PlexDiscover and
  plexBrowseLists into a shared lib/hueTile so the two surfaces can't drift.
- Document migration 0073 downgrade() as lossy and de-dup non-feed rows before
  recreating the narrow (user_id, name) constraint (verified by the drift test).
- Add unit tests for coercePlexFilters (legacy single-collection migration) and
  plexFiltersSignature (order-independence, title-ignoring).

Gate: tsc/lint/knip/prettier clean, 410 vitest; backend ruff + migration drift +
saved-views tests green.

frontend/src/components/SavedViewsProvider.tsx

@@ -140,10 +140,13 @@ export function SavedViewsProvider({ children }: { children: ReactNode }) {
     setModalOpen(false);
   }, [source]);
 
-  // Feed only: keep the default-view mirror (read on load) in sync with the server state.
+  // Feed only: keep the default-view mirror (read on load) in sync with the server state. Depend on the
+  // mirror fn (a module-stable ref, or undefined for plex) NOT the whole `cfg` object — cfg re-memoizes
+  // on every live filter edit, which would fire this synchronous localStorage write far beyond its intent.
+  const syncMirror = cfg.syncDefaultMirror;
   useEffect(() => {
-    if (viewsQuery.data) cfg.syncDefaultMirror?.(viewsQuery.data);
-  }, [viewsQuery.data, cfg]);
+    if (viewsQuery.data) syncMirror?.(viewsQuery.data);
+  }, [viewsQuery.data, syncMirror]);
 
   const currentKey = cfg.keyOf(cfg.filters);
   const activeView = useMemo(