feat(plex): port the saved-views (personal views) UI to Plex (frontend)

Plex now has the same personal-views system as the feed — the rail header icon
opens the quick-pick popover, the rail title opens the manager modal (list /
create / rename / delete / reorder / set-default / apply), and the active view
leads the chip row with a "modified" dot.

One SavedViewsProvider serves both modules: it switches `source` (feed ⟷ plex)
by the active page (both filter providers are global, so it reads whichever the
page owns) and runs the same logic on per-source wiring — the live filters,
apply, a stable signature (feed filtersToParams / plex plexFiltersSignature),
coercion (asFilters / coercePlexFilters), and what to strip on save. Moved below
PlexProvider in the tree so it can read plex state; resets sticky/modal on a
source switch. The shared popover/modal/chip are unchanged; the modal describes
a plex view's captured filters via a pure buildPlexActiveFilters (extracted from
usePlexActiveFilters — no duplication). api.savedViews/createView take a source;
`SavedView.filters` is now an opaque blob. New coercePlexFilters/plexFilters-
Signature (also dedups PlexProvider's collection migration). Empty-state copy
genericised (no longer says "feed"). A Plex view captures the rail filters (not
watch-state/sort/scope).

Verified end-to-end on localdev: create/apply/preview/default/delete on plex,
feed views stay separate + unregressed (402 vitest), no console errors.

frontend/src/lib/api/plex.ts

@@ -252,6 +252,37 @@ export const EMPTY_PLEX_FILTERS: PlexFilters = {
   keywords: [],
   collections: [],
 };
+// Coerce an opaque persisted/saved filter blob to a full PlexFilters: fill defaults for any missing
+// array/scalar, and migrate the legacy single `collection`/`collectionTitle` into the multi-select
+// `collections`/`collectionTitles`. Shared by PlexProvider (localStorage seed) and the saved-views
+// provider (a DB view blob). Not a migration — an unknown field a newer build dropped just falls away.
+export function coercePlexFilters(raw: Record<string, unknown>): PlexFilters {
+  const {
+    sortDir: _drop,
+    collection,
+    collectionTitle,
+    ...rest
+  } = raw as Record<string, unknown> & {
+    collection?: string | null;
+    collectionTitle?: string | null;
+  };
+  const merged: PlexFilters = { ...EMPTY_PLEX_FILTERS, ...(rest as Partial<PlexFilters>) };
+  if (collection && !merged.collections.length) {
+    merged.collections = [collection];
+    if (collectionTitle) merged.collectionTitles = { [collection]: collectionTitle };
+  }
+  return merged;
+}
+
+// A stable signature of a PlexFilters set (only non-default keys; display-only titles excluded), so a
+// saved view can be matched against the live filters regardless of key order — the Plex analogue of the
+// feed's filtersToParams. Reuses appendPlexFilters so the signature can't drift from the wire params.
+export function plexFiltersSignature(f: PlexFilters): string {
+  const u = new URLSearchParams();
+  appendPlexFilters(u, f);
+  return u.toString();
+}
+
 export function plexFilterCount(f: PlexFilters): number {
   return (
     f.genres.length +