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.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);