fix(ci): fail the relay preview sweep when listing PRs fails or truncates

A failed gh pr list fed an empty loop and exited 0, so a run could skip every
teardown silently. The fixed --limit 200 also dropped the oldest closed labeled
PRs without a signal. The listing now fails the step on error and fails when it
reaches the limit.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
554f456228Julius Marminge committed on 10/22/2026, 10:08:57 PMparent0d37f4b

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