feat: add batch issue inspection

[gokul-debugger]

Summary

• add contribcheck batch for newline-delimited issue references
• preserve input order while using bounded asynchronous concurrency
• retain per-item failures without discarding successful reports
• provide versioned JSON output, aggregate verdict counts, and documented exit codes

Testing

• python -m pytest (51 passed)
• ruff check .
• ruff format --check .
• mypy src tests
• git diff --check

Closes #3