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`.

tests/unit/embed_player_modal.test.mjs

@@ -0,0 +1,34 @@
+import { test } from 'node:test';
+import assert from 'node:assert';
+import { EmbedPlayerModal } from '../../js/ui/components/EmbedPlayerModal.js';
+
+// Polyfill EventTarget for Node < 16 if needed, but likely available
+if (typeof EventTarget === 'undefined') {
+    global.EventTarget = class EventTarget {
+        constructor() { this.listeners = {}; }
+        addEventListener() {}
+        removeEventListener() {}
+        dispatchEvent() { return true; }
+    };
+}
+
+test('EmbedPlayerModal interface', async (t) => {
+    const modal = new EmbedPlayerModal();
+
+    await t.test('has expected methods', () => {
+        assert.strictEqual(typeof modal.load, 'function');
+        assert.strictEqual(typeof modal.getRoot, 'function');
+        assert.strictEqual(typeof modal.getVideoElement, 'function');
+        assert.strictEqual(typeof modal.setVideoElement, 'function');
+        assert.strictEqual(typeof modal.resetStats, 'function');
+        assert.strictEqual(typeof modal.updateStatus, 'function');
+        assert.strictEqual(typeof modal.setTorrentStatsVisibility, 'function');
+        assert.strictEqual(typeof modal.addEventListener, 'function');
+        assert.strictEqual(typeof modal.removeEventListener, 'function');
+        assert.strictEqual(typeof modal.dispatch, 'function');
+    });
+
+    await t.test('resetStats is no-op and does not throw', () => {
+        assert.doesNotThrow(() => modal.resetStats());
+    });
+});