docs & dx: fix typo, improve pytest config, add security contact

[Atman36]

What

This PR bundles several small, non-breaking improvements:

1. CONTRIBUTING.md — Fix capitalization typo: Prek hooks → prek hooks
2. pytest.ini — Add testpaths and pythonpath for better test discovery
3. SECURITY.md — Add email contact for sensitive security issues
4. exception.py — Remove redundant pass statements and add __all__ declaration

Why

• Consistency: Fix typo to match the tool's actual name
• DX: Explicit pytest paths reduce command-line arguments needed
• Security: Provide direct contact channel for sensitive reports
• Code quality: Explicit exports improve IDE support and follow Python best practices

How to verify

# Check syntax
python3 -m py_compile src/kimi_cli/exception.py

# Verify __all__ exports
python3 -c "from kimi_cli.exception import __all__; print(__all__)"

Notes

• Breaking change: No
• Risk: Low
• Files changed: 4
• Total lines: ~30 (net reduction due to removed pass statements)

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PR prepared with AI assistance (Claude Code)

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 3 additional findings.