docs: restructure guideline and expand content for 2025/2026

[Ali-Yazdani]

Refactor the documentation structure to a more logical hierarchy and significantly expand the technical depth of the DevSecOps guidelines.

Key changes include:

• Restructured the directory hierarchy for better organization of People, Process, and Governance pillars.
• Added comprehensive new sections on modern security concerns:
  • Software Supply Chain Security (SBOM, Artifact Signing, Provenance, and CI/CD Pipeline Security).
  • AI Governance and Risk (AI in the SDLC and AI in products).
  • Application Security Posture Management (ASPM).
• Expanded existing documentation with deep dives into:
  • Secure Design and Requirements.
  • IDE and AI-assisted development security.
  • Infrastructure as Code (IaC) scanning.
  • Container hardening and cloud-native security (CNAPP).
  • API security (OWASP API Top 10).
  • Mobile application security (OWASP MAS).
  • Vulnerability management and risk-based prioritization.
• Updated all core documentation to reflect current industry standards and frameworks (NIST SSDF, SLSA, OWASP SAMM/DSOMM).
• Archived previous versions into the old-versions/V0.3/ directory to maintain historical context.
• Updated the README and Table of Contents to reflect the new structure.