fix(home): shelf honours the Plex gate; hero unpins its origin; palette asks for a surprise

- A13: with Plex off, the Home shelf and the hero's comfort tier go YouTube-only like the rails
  beside them (owner's call: hide the tiles). The pins are kept; GET /pins still lists them.
- Reorder deals the listed pins into the slots they already hold, so a partial list (hidden Plex
  pins, a stale tab) no longer puts two pins on one position; repeats are ignored.
- A21: a comfort hero carries `pinned_from`, the shelf entry it was resolved from; its menu acts on
  that pin, so a pinned show's next episode offers "Unpin" instead of creating a second pin.
- B12: the palette's "Meglepetés" asks for the surprise tier (the next press leading with it); the
  rotation carries on from there.
- B13: the surprise token names the history entry it was requested for (minted by setPage's new
  `then`, after the push) and is dropped on any other entry, so a navigation that never mounted
  Home cannot replay it later.

frontend/src/lib/api/discover.ts

@@ -15,6 +15,9 @@ export type DiscoverBudget = (typeof DISCOVER_BUDGETS)[number];
 // Where the hero came from. Travels with the card so the page can label it honestly instead of
 // inferring "where you left off" over something the user has never opened.
 export type HeroTier = "resume" | "comfort" | "surprise";
+/** The server's tier order (`app/discover/hero.py::HERO_TIERS`): a reroll's press count `start`
+ *  leads with `HERO_TIERS[start % 3]`, which is how a press can ASK for a tier. */
+export const HERO_TIERS: readonly HeroTier[] = ["resume", "comfort", "surprise"];
 
 export type DiscoverKind = "video" | "movie" | "show" | "episode" | "channel" | "playlist";
 
@@ -43,6 +46,10 @@ export interface DiscoverCard {
   plex: PlexCard | null;
   // Shelf entries only.
   pin_id?: number;
+  /** A comfort-tier hero only: the shelf entry it was resolved from — for a pinned SHOW, the show
+   *  whose next episode this is. The hero's pin row acts on it rather than on the episode, which is
+   *  not itself pinned (`app/discover/pins.py::playables`). */
+  pinned_from?: Pick<DiscoverCard, "source" | "kind" | "id" | "title">;
   /** What actually plays when the tile is clicked: a show's next episode, a channel's newest
    * unwatched video, or a copy of the tile itself when it plays directly. Null when the pin has
    * nothing to offer right now (a fully-watched channel, an empty playlist). */