Fix no-traffic deployment readback

[Pigbibi]

Summary

• compare effective nonzero Cloud Run traffic only
• accept the expected zero-percent candidate revision
• keep readback output and persisted baseline non-sensitive

Validation

• actionlint
• static workflow/readback tests
• git diff --check

The predecessor no-traffic workflow stopped before any traffic, Scheduler, IAM, configuration, cleanup, endpoint, gateway, or broker mutation.