fix: minimize native check evaluation payload

[kazukinakai]

Summary

• pass only the four fields required to evaluate repository-native checks
• prevent the check-run payload from exceeding the process environment limit
• retain exact context and workflow-path anti-spoof validation
• pin caller and implementation to the reviewed fix commit

Production evidence

The agiletec canary found both successful native checks, then failed with Argument list too long while passing the full 100-check API payload through CHECK_RUNS.

Verification

• python3 -m unittest discover -s tests (37 passed)
• shell and Node syntax checks
• actionlint v1.7.7
• git diff --check