feat(player): guard against audio playback on secondary device

frontend/angular/src/app/features/player/player-shell.component.spec.ts

@@ -350,4 +350,29 @@ describe('PlayerShellComponent gameplay wiring', () => {
 
     component.ngOnDestroy();
   });
+
+  it('installs secondary-device audio guard while player shell is mounted', async () => {
+    const originalPlay = vi.fn().mockRejectedValue(new Error('original play'));
+    const mediaPrototype = { play: originalPlay };
+
+    vi.stubGlobal('window', {
+      location: { hash: '', search: '' },
+      history: { state: null, replaceState: vi.fn() },
+      localStorage: { getItem: vi.fn().mockReturnValue('en'), setItem: vi.fn(), removeItem: vi.fn() },
+      sessionStorage: { getItem: vi.fn().mockReturnValue(null), setItem: vi.fn(), removeItem: vi.fn() },
+      HTMLMediaElement: { prototype: mediaPrototype },
+      addEventListener: vi.fn(),
+      removeEventListener: vi.fn(),
+    });
+    vi.stubGlobal('navigator', { language: 'en-US', onLine: true });
+
+    const component = new PlayerShellComponent();
+    component.ngOnInit();
+
+    await expect(mediaPrototype.play()).resolves.toBeUndefined();
+
+    component.ngOnDestroy();
+
+    await expect(mediaPrototype.play()).rejects.toThrow('original play');
+  });
 });