fix(e2e): use button role for storage classes sidebar link in rook plugin

The storage classes sidebar entry is a button, not a link. Using getByRole('link')
caused the test to fail with 'element not found'. Switch to getByRole('button')
which matches the actual Headlamp sidebar structure.

Also increased timeout from 10s to 15s for consistency with other waits.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

e2e/rook.spec.ts

@@ -44,8 +44,12 @@ test.describe('Rook plugin smoke tests', () => {
     await page.goto('/c/main/rook-ceph');
 
     const sidebar = page.getByRole('navigation', { name: 'Navigation' });
-    const storageClassesLink = sidebar.getByRole('link', { name: /storage classes/i });
-    await expect(storageClassesLink).toBeVisible({ timeout: 10_000 });
+    const rookBtn = sidebar.getByRole('button', { name: /rook/i });
+    await rookBtn.click();
+    await page.waitForLoadState('networkidle');
+
+    const storageClassesLink = sidebar.getByRole('button', { name: /storage classes/i });
+    await expect(storageClassesLink).toBeVisible({ timeout: 15_000 });
     await storageClassesLink.click();
 
     await page.waitForLoadState('networkidle');