fix(embed): implement robust EmbedPlayerModal and guard resetTorrentStats

- Add `js/ui/components/EmbedPlayerModal.js` to implement the `VideoModal` interface for embed contexts (including `resetStats`).
- Update `js/ui/ModalManager.js` to detect embed mode and use `EmbedPlayerModal`.
- Clean up `js/embed.js` to remove local modal definition and add `postMessage` diagnostic logging.
- Update `js/app.js` `resetTorrentStats` log message and verify guard.
- Add unit tests for `EmbedPlayerModal` and `resetTorrentStats` logic.
- Add E2E reproduction script `tests/e2e/repro_issue.spec.ts`.

js/app.js

@@ -4906,7 +4906,7 @@ class Application {
         this.videoModal.resetStats();
       } else {
         devLogger.info(
-          "[Application] resetTorrentStats: videoModal.resetStats not available in this context — skipping."
+          "[Application] resetTorrentStats: videoModal.resetStats not available — skipping."
         );
       }
     }