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/App.tsx

@@ -268,7 +268,7 @@ export default function App() {
   // greeted you with a stale query (colliding with a persisted collection filter → confusing
   // "0 matches") after a reload. Kept in App so it survives page switches within a session, but
   // resets on reload.
-  const [plexQ, setPlexQ] = useState("");
+  const [plexQ, setPlexQ] = useAccountPersistedState(LS.plexQ, ""); // survives F5, unlike the feed search
   // Bumped to tell the channel manager to drop a stale column filter when we send the user
   // there to see a specific set (the header's "without full history" link).
   const [channelsFilterReset, setChannelsFilterReset] = useState(0);