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/components/PlexMenu.dom.test.tsx

@@ -179,11 +179,18 @@ describe("a Plex title's menu", () => {
   });
 
   it("a started show continues, and starts its episode over from the next row", () => {
-    setup(card({ type: "show", status: "in_progress" }));
+    setup(card({ type: "show", status: "in_progress", resumable: true }));
     rightClick();
     expect(labels().slice(0, 2)).toEqual(["card.continue", "card.restartTitle"]);
   });
 
+  it("a part-watched show with no episode to resume plays, with nothing to start over", () => {
+    setup(card({ type: "show", status: "in_progress", resumable: false }));
+    rightClick();
+    expect(labels()[0]).toBe("plex.play");
+    expect(labels()).not.toContain("card.restartTitle");
+  });
+
   it("the card's '…' opens the same menu, and says so", () => {
     setup(card({}));
     const hoverMore = moreButtons()[0]!;