Secure code review cheat sheet (#1861)

* Add Secure Code Review Cheat Sheet with methodology and checklists

* Enhance Secure Code Review cheat sheet with manual review methodology

- Add clear distinction between baseline and diff-based reviews
- Expand preparation guidance for both review types
- Include manual review focus areas and techniques
- Clarify automated tool integration as supporting manual analysis
- Update SDLC integration timing for different review approaches
- Simplify structure for better readability and practical use

* Fix markdown linting violations in Secure Code Review Cheat Sheet

* Fix broken/deprecated external links

* Clean additional resources and fix lint issues

Author: ZMelliti