test: open a folder before reaching its rows (the tree draws them lazily)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

test/e2e-cover.test.cjs

@@ -88,6 +88,8 @@ app.whenReady().then(async () => {
     check('...and the front matter still names it', /cover: dropped\.png/.test(fm('Folder/Note.md')));
 
     // back to a gradient
+    await js(`document.querySelector('.row[data-id="Folder"]')?.dispatchEvent(new KeyboardEvent('keydown', { key: 'ArrowRight', bubbles: true }))`); // folders draw their rows when first opened
+    await sleep(400);
     await js(`document.querySelector('.row[data-id="Folder/Note"], .row[data-id="Folder"]')?.click()`);
     await sleep(600);
     await js(`await new Promise((r) => setTimeout(r, 200))`);