fix: pass jobs_json via env var to fix stdin conflict in drift-to-issue

[fullstackjam]

Summary

• echo "$jobs_json" | python3 - <<'PY' is broken: the heredoc and pipe both compete for stdin. Python reads the script from the heredoc, leaving sys.stdin.read() to return an empty string, which causes json.JSONDecodeError on every run.
• Fix: pass the JSON via JOBS_JSON env var and read it with os.environ["JOBS_JSON"] instead.

This is why drift-to-issue: All jobs have failed emails fire on every Harness run.

Test plan

• Merge and verify the next Harness workflow run triggers drift-to-issue without error

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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