fix(plex): a Restart does not replay on a reload or a Forward onto the player

fromStart rode in history.state._sub, so reloading the player entry restarted
the item from 0 again and the progress checkpoint overwrote its resume point.
A sub-view config can now say what the history entry keeps of a view.

frontend/src/components/plexSubUrl.test.ts

@@ -76,3 +76,18 @@ describe("PLEX_SUB_URL decode guards", () => {
     expect(U.decode("")).toBeNull();
   });
 });
+
+describe("PLEX_SUB_URL entry", () => {
+  // E28 review E1: the Restart click must not replay on a reload / Forward onto the player entry.
+  it("keeps the player without its one-shot fromStart, and every other view whole", () => {
+    const entry = U.entry!;
+    expect(entry({ kind: "player", id: "7", queue: ["7", "8"], fromStart: true })).toEqual({
+      kind: "player",
+      id: "7",
+      queue: ["7", "8"],
+      fromStart: undefined,
+    });
+    const info = { kind: "info", id: "7" } as const;
+    expect(entry(info)).toBe(info);
+  });
+});

frontend/src/components/plexSubUrl.ts

@@ -49,6 +49,10 @@ export const PLEX_SUB_URL: SubviewUrl<Sub> = {
         return null; // discover (root) + the ephemeral player are not URL-mirrored
     }
   },
+  // `fromStart` is the Restart CLICK, not a property of the entry: kept in history.state it restarted
+  // the item from 0 again on every reload or Forward onto the player, and the progress checkpoint
+  // then overwrote the resume point it had skipped (E28 review E1).
+  entry: (v) => (v.kind === "player" && v.fromStart ? { ...v, fromStart: undefined } : v),
   decode: (raw) => {
     const i = raw.indexOf(":");
     const kind = i === -1 ? raw : raw.slice(0, i);