Fixes two real bugs found during testing:
- Profile/hashtag/status pages showing "No items found" were wrongly
treated as a successful redirect. Now detected via Nitter's own
timeline-none marker and triggers fallback to the next instance. - If page inspection failed (e.g. an instance showing a bot-check
challenge, or a broken/502 page), the extension gave up entirely
instead of trying the next instance. Now it correctly falls back.
Also removed nuku.trabun.org from the instance list (consistently
down/broken).