Add asset availability check before updating demo server. The workflow now waits
up to 5 minutes for checksums.txt and the linux-amd64 tarball to be available
before attempting the update. This prevents the install script from failing when
the release is published before all assets finish uploading.
Resolves demo server downtime during releases.
The workflow was failing because /api/state requires authentication,
but the verification step was making an unauthenticated request.
Changes:
- Authenticate with demo/demo credentials before checking node count
- Use jq for cleaner JSON parsing instead of grep/cut
- Check total node count from API response instead of regex pattern matching
Related to user report about demo server not updating to 4.26.3.
The demo server was actually updated successfully, but the workflow
marked itself as failed due to the verification check failing.
