test(dashboard): cover combined edit+standalone URL params

Adds the React-side analogue of the legacy `?edit=true&standalone=true`
Cypress mount, asserting the two URL params remain orthogonal:
standalone=2 hides DashboardHeader while editMode still drives the
`dashboard--editing` wrapper class. Satisfies sc-107447 task 3.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

superset-frontend/src/dashboard/components/DashboardBuilder/DashboardBuilder.test.tsx

@@ -165,6 +165,42 @@ describe('DashboardBuilder', () => {
     expect(header).toBeInTheDocument();
   });
 
+  test('should hide DashboardHeader when standalone mode hides nav and title (?standalone=2)', () => {
+    // React-level equivalent of the legacy `cy.get('#app-menu').should('not.exist')`
+    // Cypress assertion. The `#app-menu` node lives in Flask's spa.html template,
+    // gated by `{% if standalone_mode %}`, so RTL cannot reach it directly.
+    // `?standalone=2` maps to DashboardStandaloneMode.HideNavAndTitle, which the
+    // DashboardBuilder honours by suppressing the React-side DashboardHeader.
+    const originalHref = window.location.href;
+    window.history.replaceState({}, '', '/?standalone=2');
+    try {
+      const { queryByTestId } = setup();
+      expect(queryByTestId('dashboard-header-container')).not.toBeInTheDocument();
+    } finally {
+      window.history.replaceState({}, '', originalHref);
+    }
+  });
+
+  test('should apply editing class and hide header when both edit and standalone params are set', () => {
+    // Combined-params analogue of the legacy `?edit=true&standalone=true` Cypress
+    // mount. The two URL params are orthogonal on the React side: standalone=2
+    // suppresses DashboardHeader regardless of editMode, while editMode still
+    // drives the `dashboard--editing` class on the wrapper.
+    const originalHref = window.location.href;
+    window.history.replaceState({}, '', '/?edit=true&standalone=2');
+    try {
+      const { getByTestId, queryByTestId } = setup({
+        dashboardState: { ...mockState.dashboardState, editMode: true },
+      });
+      expect(getByTestId('dashboard-content-wrapper')).toHaveClass(
+        'dashboard dashboard--editing',
+      );
+      expect(queryByTestId('dashboard-header-container')).not.toBeInTheDocument();
+    } finally {
+      window.history.replaceState({}, '', originalHref);
+    }
+  });
+
   test('should render a Sticky top-level Tabs if the dashboard has tabs', async () => {
     const { findAllByTestId } = setup({
       dashboardLayout: undoableDashboardLayoutWithTabs,