Add CI/CD improvements: Prettier, Husky, security scanning, and AGENTS.md

[abhishyantkhare]

Summary

This PR adds comprehensive CI/CD and documentation improvements to the Ghost repository:

• ✨ Prettier configuration for consistent code formatting across the codebase
• 🔧 Enhanced lint-staged to run ESLint and Prettier on staged files
• 🤖 Dependabot configuration for automated weekly dependency updates
• 🔒 Security scanning workflow with npm audit and CodeQL analysis
• 🛡️ Enhanced .gitignore with security-sensitive file patterns
• 📚 Comprehensive AGENTS.md with AI coding agent guidelines

Files Created/Modified

New Files

• .prettierrc - Prettier configuration (single quotes, 4-space tabs, trailing commas)
• .prettierignore - Excludes build artifacts, node_modules, generated files
• .github/dependabot.yml - Weekly npm dependency updates with grouping
• .github/workflows/security.yml - Security scanning (npm audit + CodeQL)

Modified Files

• package.json - Added prettier dependency and enhanced lint-staged config
• .gitignore - Added patterns for secrets and sensitive files
• AGENTS.md - Comprehensive AI agent guidelines (separate from CLAUDE.md)

Test Plan

• Verify Prettier configuration works: npx prettier --check .
• Verify lint-staged runs on commit (on main branch)
• Verify Dependabot creates dependency update PRs
• Verify security workflow runs on push/PR to main
• Review AGENTS.md content for accuracy

Notes

• The existing Husky setup in .github/hooks/ is preserved
• lint-staged now runs both ESLint and Prettier on JS/TS files
• Security scanning runs weekly on Monday and on PRs to main
• AGENTS.md is now a standalone file with AI-specific guidelines