feat(observe): measure eligibility to runner start

[rldyourmnd]

Summary

• define exact per-job eligibility-to-runner-start SQL from durable pre-start queue spans
• exclude execution time and GitHub workflow DAG wait
• include exact workflow run and job-name correlation fields
• add the query to the fleet correlation dashboard contract

Verification

• focused queue/query tests
• full make verify
• direct live OpenObserve trace query accepted with type=traces and returned natural rows

Progresses #174.