Cardano Updates

The debug echo inside poll_github() was captured by the command
substitution `conclusion=$(poll_github)`, making `conclusion` a
multi-line string that never matched the `success)` or `failure)`
patterns in the case statement. This caused the action to always
fall through to the `*` wildcard and wait until timeout.

Redirect both debug echo lines to stderr (`>&2`) so only the
actual gh api result is captured in the return value.

- Add timeout input (default: 3600s / 1 hour), exit code 2 on timeout
- Add max-delay input (default: 300s) to cap exponential backoff
- Exponential backoff: start at delay, double each iteration, cap at max-delay
- Fix multi-value conclusion from paginated API results (tail -1)
- Add iteration counter and elapsed time to all log messages
- Use GitHub Actions error annotations for validation/timeout failures