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/components/NavigationProvider.tsx

@@ -57,13 +57,16 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
   channelViewRef.current = channelView;
 
   const setPage = useCallback(
-    (next: Page) =>
+    (next: Page, then?: () => void) =>
       // Never under an open overlay — see the interface doc. The refs are read when the push
       // actually happens, which over an open player is a moment after this call.
       closeOverlaysThenNavigate(() => {
         // A channel page overlays the content column, so a nav click must close it even when the
         // underlying page is unchanged (e.g. "Feed" while a channel opened from the feed).
-        if (next === pageRef.current && !channelViewRef.current) return;
+        if (next === pageRef.current && !channelViewRef.current) {
+          then?.();
+          return;
+        }
         setChannelView(null); // leave any open channel page when navigating via the rail
         setPageState(next);
         setAccountRaw(PAGE_KEY, next);
@@ -95,6 +98,7 @@ export function NavigationProvider({ children }: { children: ReactNode }) {
           }),
         );
         notifyNav();
+        then?.();
       }),
     [],
   );