feat(plex): a Surprise reshuffle deals the previous draw last

The rail draws three unseen titles per kind under the sidebar filters; on a
small filtered pool every reshuffle dealt the same few again. The redraw now
sends the draw on screen (exclude=), the server deals the rest of the pool
first and tops up from the excluded titles only when the pool is short, so a
small pool still fills the rail. (The two discover.py baseline entries went
with the rewritten draw.)

frontend/src/lib/api/plex.ts

@@ -625,15 +625,17 @@ export const plexApi = {
     return req(`/api/plex/discover?${u.toString()}`);
   },
   // A fresh random sample for the Surprise-me rail — a new draw every call (the ↻ refetch), narrowed by
-  // the active filters like the other rails.
+  // the active filters like the other rails. `exclude` is the previous draw: dealt last, not first.
   plexSurprise: (
     scope: string,
     limit?: number,
     filters?: PlexFilters,
     lang?: string,
+    exclude: string[] = [],
   ): Promise<{ scope: string; items: PlexCard[] }> => {
     const u = new URLSearchParams({ scope });
     if (limit) u.set("limit", String(limit));
+    for (const id of exclude) u.append("exclude", id);
     if (lang === "hu") u.set("lang", "hu");
     if (filters) appendPlexFilters(u, filters);
     return req(`/api/plex/surprise?${u.toString()}`);