fix(plex): Restart only where an episode has a resume point; the Surprise draw is re-read, not redrawn

Show cards carry resumable (ShowState, from the same rollup) so a part-watched
show whose next episode is untouched offers Play, not a Continue and a Restart
that do the same thing; plexStarted is the one rule for cards and menus. The
Surprise rail's key sits under the discover root: whatever refreshes the rails
re-reads the draw (keep=) with its watch state now, kept past the 5-minute gc,
and only the reshuffle deals. Closing the player refreshes the Discover rails.
A show card's play acts on the last click only, and only where it was made.

frontend/src/lib/queryKeys.test.ts

@@ -89,12 +89,13 @@ describe("qk — variadic composite plex keys", () => {
       FILTERS,
     ]);
     expect(qk.plexSurprise("movie", "hu", FILTERS)).toEqual([
-      "plex-surprise",
+      "plex-discover",
+      "surprise",
       "movie",
       "hu",
       FILTERS,
     ]);
-    // A bare call stays a prefix for the reshuffle/watched-toggle invalidations.
-    expect(qk.plexSurprise()).toEqual(["plex-surprise"]);
+    // Under the discover root: whatever refreshes the rails refreshes the draw's cards too.
+    expect(qk.plexSurprise()).toEqual(["plex-discover", "surprise"]);
   });
 });