Fix flaky prefetch-runtime test by waiting for elements
The "includes root params, but not dynamic content" test was timing out
due to race conditions. Added explicit waits for link elements to be
visible after each checkbox click and after browser.back(), ensuring
the UI is ready before proceeding to the next interaction.
Waits added:
- After first act(): Wait for "en" link to confirm prefetch completed
- After second act(): Wait for "de" link to confirm prefetch completed
- After browser.back(): Wait for "de" link before navigation
