Add comprehensive security guide chapters and modernize existing content

[abhishek-anand]

Summary

• Added 15 new security chapters covering authentication, authorization, cryptography, and modern threats
• Updated HTTPS configuration with TLS 1.3 recommendations and modern cipher suites
• Enhanced security checklist with current best practices and additional security headers
• Added AI/LLM security chapter addressing prompt injection and model security
• Improved README with proper chapter links and updated structure
• Updated vulnerability examples with recent high-profile breaches (2020-2024)

Changes Made

• New Chapters: authentication.md, authorization.md, cryptography.md, passwords.md, sessions.md, security-headers.md, attacks.md, configuration-security.md, data-validation.md, public-key-cryptography.md, security-libraries.md, security-hygiene.md, ai-security.md, security-usability.md, security-checklist-explained.md
• Updated Content: https.md with modern TLS configurations, security-checklist.md with 2025 best practices, what-can-go-wrong.md with recent breach examples
• Enhanced Structure: README.md with proper navigation links and updated chapter organization

Test Plan

• Verify all chapter links work correctly
• Review technical accuracy of security recommendations
• Check formatting and readability across all new chapters
• Validate code examples and configuration snippets