improvement(scroll): fade every capped list's clipped edges

The sweep's own three (the thread, the Plex collections filter, the tag manager)
plus the seven the spec missed — the playlist picker, the row tag menu, the Plex
playlist/collection dialogs, the player's track menu, the video description and
the table's multi-select filter. Same idiom throughout: a height-capped list that
silently clipped its content now says so, and hides its scrollbar like the rail
and the panels already do.

The table's option list is its own module-level component because it owns a hook:
FilterPopover is redeclared per DataTable render, so React remounts it.

frontend/src/components/PlexSidebar.tsx

@@ -5,6 +5,7 @@ import { Layers, ListMusic, Plus, SlidersHorizontal, X } from "lucide-react";
 import { api, EMPTY_PLEX_FILTERS, plexFilterCount, type PlexFilters } from "../lib/api";
 import { defaultLayout, type PanelLayout } from "../lib/panelLayout";
 import { useDebounced } from "../lib/useDebounced";
+import { useScrollFade } from "../lib/useScrollFade";
 import SidePanel from "./SidePanel";
 import PanelGroups, { type PanelItem } from "./PanelGroups";
 
@@ -56,6 +57,7 @@ export default function PlexSidebar({
   onToggleCollapse,
 }: Props) {
   const { t } = useTranslation();
+  const collFade = useScrollFade();
   const playlistsQ = useQuery({ queryKey: ["plex-playlists"], queryFn: () => api.plexPlaylists() });
   const [newPlaylist, setNewPlaylist] = useState("");
   const [editing, setEditing] = useState(false);
@@ -258,7 +260,11 @@ export default function PlexSidebar({
             placeholder={t("plex.filter.collectionSearch")}
             className="mb-1.5 w-full rounded-lg border border-border bg-card px-2 py-1 text-sm focus:border-accent focus:outline-none"
           />
-          <div className="flex max-h-56 flex-col gap-0.5 overflow-y-auto">
+          <div
+            ref={collFade.ref}
+            style={collFade.style}
+            className="flex max-h-56 flex-col gap-0.5 overflow-y-auto no-scrollbar"
+          >
             {collections.map((c) => (
               <button
                 key={c.id}