fix(ci): replace invalid job-level secrets gate with step-level gate in commercial-backup.yml

[Coding-Dev-Tools]

GitHub Actions does not support the secrets context in job-level if expressions, causing the workflow to fail every scheduled run. Replace with the same step-level gate pattern used in production-synthetics.yml: a dedicated gate step checks env vars and sets skip=true when secrets are unconfigured (pre-GA), with all subsequent steps conditioned on steps.gate.outputs.skip != 'true'.

[Coding-Dev-Tools]

Pre-PR Review — APPROVE

Verdict: APPROVE

Analysis

This PR correctly replaces the invalid job-level if: ${{ secrets.ENGRAPHIS_CUSTOMER_URL != '' }} gate (which GitHub Actions evaluates as an empty string in if expressions, causing the job to always fail) with a proper step-level gate that checks all four required secrets and sets a skip output.

Verification

• CI: 7/8 checks pass (docker build correctly skips — no Dockerfile changes)
• The fix is minimal, correct, and follows GitHub Actions best practices
• No security concerns — secrets are checked for presence only, never exposed
• The ::warning:: annotation provides clear visibility when secrets are missing

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Hermes Pre-PR Reviewer — 2026-07-21