fix(plex): series-page UX fixes from UAT (7 items)

1. Series detail pages now match the movie info page: the customize menu lives in the
   hero panel (top-right), the Cast/Seasons/Related strips sit in glassy panels, and the
   menu is dynamic — Related shows can be toggled (new plexInfoRelated pref).
2. The Plex search box now survives F5 (persisted per-account like the filters).
3. Show + season hero posters get a hover Play/Resume overlay.
4. Card top-right watched toggle can now UN-watch: the watched/in-progress badges were
   intercepting the click (no pointer-events-none), so the toggle underneath never fired.
5. Episode card: the watched check no longer jumps on hover (badge now shares the
   toggle's box); every card's title/meta gets its own glassy translucent background and
   the Add-to-playlist button is always visible (not hover-only).
6. Season-card 'In progress' label is readable again (solid dark badge over the poster).
7. On a season page the show title is clickable → back to the show (history-correct).

frontend/src/lib/plexDetailUi.tsx

@@ -15,9 +15,11 @@ export function useDetailPrefs() {
   const prefs = (qc.getQueryData<{ preferences?: Record<string, unknown> }>(["me"])?.preferences ?? {}) as {
     plexInfoArtBg?: boolean;
     plexInfoCast?: boolean;
+    plexInfoRelated?: boolean;
   };
   const [artBg, setArtBg] = useState(prefs.plexInfoArtBg !== false);
   const [showCast, setShowCast] = useState(prefs.plexInfoCast !== false);
+  const [showRelated, setShowRelated] = useState(prefs.plexInfoRelated !== false);
   const save = (patch: Record<string, unknown>) => {
     api.savePrefs(patch).catch(() => {});
     qc.setQueryData<{ preferences?: Record<string, unknown> } | undefined>(["me"], (m) =>
@@ -27,6 +29,7 @@ export function useDetailPrefs() {
   return {
     artBg,
     showCast,
+    showRelated,
     toggleArtBg: () => {
       const next = !artBg;
       setArtBg(next);
@@ -37,6 +40,11 @@ export function useDetailPrefs() {
       setShowCast(next);
       save({ plexInfoCast: next });
     },
+    toggleRelated: () => {
+      const next = !showRelated;
+      setShowRelated(next);
+      save({ plexInfoRelated: next });
+    },
   };
 }
 
@@ -75,12 +83,18 @@ export function DetailCustomizeMenu({
   showCast,
   onToggleCast,
   hasCast,
+  showRelated,
+  onToggleRelated,
+  hasRelated,
 }: {
   artBg: boolean;
   onToggleArtBg: () => void;
   showCast: boolean;
   onToggleCast: () => void;
   hasCast: boolean;
+  showRelated?: boolean;
+  onToggleRelated?: () => void;
+  hasRelated?: boolean;
 }) {
   const { t } = useTranslation();
   const [open, setOpen] = useState(false);
@@ -105,6 +119,9 @@ export function DetailCustomizeMenu({
         >
           <PrefToggle label={t("plex.info.prefArtBg")} on={artBg} onClick={onToggleArtBg} />
           {hasCast && <PrefToggle label={t("plex.info.prefCast")} on={showCast} onClick={onToggleCast} />}
+          {hasRelated && onToggleRelated && (
+            <PrefToggle label={t("plex.info.prefRelated")} on={showRelated ?? true} onClick={onToggleRelated} />
+          )}
         </div>
       )}
     </div>

frontend/src/lib/storage.ts

@@ -27,6 +27,7 @@ export const LS = {
   plexShow: "siftlode.plexShow",
   plexSort: "siftlode.plexSort",
   plexFilters: "siftlode.plexFilters",
+  plexQ: "siftlode.plexQ",
   plexPlaylistLayout: "siftlode.plexPlaylistLayout",
   notifHistory: "siftlode.notifications",
   notifSettings: "siftlode.notifSettings",