fix: address final review findings (order-notification watcher robustness)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/features/admin/shell/admin-layout.component.spec.ts

@@ -30,6 +30,7 @@ describe('AdminLayoutComponent notifications bell', () => {
     recentOrders: ReturnType<typeof signal<AdminOrder[]>>;
     unreadCount: ReturnType<typeof signal<number>>;
     start: jasmine.Spy;
+    stop: jasmine.Spy;
     markAllSeen: jasmine.Spy;
   };
 
@@ -38,6 +39,7 @@ describe('AdminLayoutComponent notifications bell', () => {
       recentOrders: signal<AdminOrder[]>([makeOrder('o1', '1001')]),
       unreadCount: signal(1),
       start: jasmine.createSpy('start'),
+      stop: jasmine.createSpy('stop'),
       markAllSeen: jasmine.createSpy('markAllSeen'),
     };
 
@@ -73,4 +75,11 @@ describe('AdminLayoutComponent notifications bell', () => {
     expect(component.notificationsOpen()).toBe(false);
     expect(watcherStub.markAllSeen).toHaveBeenCalledTimes(1);
   });
+
+  it('stops the watcher when the component is destroyed', () => {
+    const fixture = TestBed.createComponent(AdminLayoutComponent);
+    fixture.detectChanges();
+    fixture.destroy();
+    expect(watcherStub.stop).toHaveBeenCalledTimes(1);
+  });
 });