Fixed post-commit hook to properly escape JSON payloads using python.
Previous implementation was vulnerable to breaking on commit messages
with special characters (quotes, newlines, etc.).
CHANGES:
- Use python json.dumps() for proper JSON escaping
- Prevents 422 validation errors from coordination API
- Handles multi-line commit messages correctly
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>