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/plexCards.dom.test.tsx

@@ -200,7 +200,7 @@ describe("PlexPosterCard with a next episode", () => {
     const onRestart = vi.fn();
     render(
       <PlexPosterCard
-        card={{ ...show, status: "in_progress" }}
+        card={{ ...show, status: "in_progress", resumable: true }}
         onOpen={onOpen}
         onRestart={onRestart}
       />,
@@ -211,6 +211,19 @@ describe("PlexPosterCard with a next episode", () => {
     expect(onOpen).toHaveBeenCalledTimes(1);
   });
 
+  it("plays a part-watched show with no episode to resume, with no Restart beside it", () => {
+    // Its next episode is untouched: Continue and Restart would both play it from its start.
+    render(
+      <PlexPosterCard
+        card={{ ...show, status: "in_progress", resumable: false }}
+        onOpen={vi.fn()}
+        onRestart={vi.fn()}
+      />,
+    );
+    expect(screen.queryByRole("button", { name: "card.restart" })).toBeNull();
+    expect(screen.queryByRole("button", { name: "card.continue" })).toBeNull();
+  });
+
   it("names the episode it would play once its preview is up, and not asked before", async () => {
     vi.useFakeTimers();
     const ask = vi