fix(plex): a collection sibling is a full Plex card, and the player's info overlay plays it

- PlexInfo's collection strip gives each card the related strip's action set: the "…" menu (with
  Restart for a touch reader), the watched toggle and the playlist add.
- `onPlayItem` is required, so no variant draws a Play that does nothing; the player's info overlay
  plays the sibling in the running player (`go(id, _, fromZero)` for its Restart).

frontend/src/components/PlexPlayer.controls.dom.test.tsx

@@ -312,6 +312,47 @@ describe("a double-tap on a side third skips 10 s (C5)", () => {
   });
 });
 
+// E28 review D1: the info overlay drew its collection siblings with a Play that did nothing — the
+// overlay had no way to play one. It plays it in this player, at its resume point or from the start.
+describe("a collection sibling in the info overlay", () => {
+  const withSibling = (id: string): PlexItemDetail => ({
+    ...item(id),
+    cast: [],
+    genres: [],
+    directors: [],
+    collections: [
+      {
+        id: "c1",
+        title: "Saga",
+        source: "plex",
+        items: [
+          {
+            id: "B",
+            type: "movie",
+            title: "Title B",
+            thumb: "",
+            status: "in_progress",
+            position_seconds: 300,
+            duration_seconds: 3000,
+          },
+        ],
+      },
+    ],
+  });
+
+  it("plays its Restart in this player, from the start", { timeout: 10000 }, async () => {
+    const { session } = mount({ details: { A: withSibling("A"), B: item("B", 300) } });
+    await playingAt("/media/A", 100);
+    fireEvent.click(screen.getByLabelText("plex.player.more"));
+    fireEvent.click(await menuItem("plex.player.infoBtn"));
+    // The overlay is a lazy chunk: its first import takes a while under the test runner.
+    const restart = await screen.findByRole("button", { name: "card.restart" }, { timeout: 5000 });
+    fireEvent.click(restart);
+    await waitFor(() => expect(lastStart(session)).toEqual(["B", 0]));
+    expect(screen.queryByRole("heading", { name: "Saga" })).toBeNull(); // the overlay closed
+  });
+});
+
 describe("the C5 row", () => {
   it("has no Stop, Restart or ±10 s buttons, and keeps the rare tools behind the ⋯", async () => {
     mount({ details: { A: item("A") } });