Add a feed no longer asks for a folder (#201)

A feed's settings stopped showing its folder in 0.10.3; the dialog that adds one
still asked for it. The API keeps its folder for scripts.

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

tests/ui/app.spec.js

@@ -948,6 +948,8 @@ test('the Directory lists what everyone here reads, the most subscribed first, b
   await piper.locator('#addFeed').click();
   await expect(piper.locator('#nurl')).toBeVisible();
   await expect(piper.locator('#modalCard .tile, #modalCard .rank')).toHaveCount(0);
+  // Nor a folder: a feed's folder is its title (#201).
+  await expect(piper.locator('#nfolder')).toHaveCount(0);
   await piper.locator('#modalCard button[title="Cancel"]').click();
 
   const row = async () =>