feat: Add Security Gates guide for DevSecOps roadmap

[bobbyonmagic]

Fixes #750 (Security Gates skill)

Adds comprehensive guide covering:

• Policy as Code with OPA and Kyverno
• Vulnerability Gates with Trivy, Grype, and Snyk
• Compliance Gates with Checkov (PCI-DSS, SOC 2, CIS Benchmarks)
• CI/CD Integration with complete GitHub Actions, GitLab CI, and Jenkins examples

Content:

• 2,842 total lines across 5 files
• Real-world examples: Target breach, Equifax breach, Capital One breach
• Production-ready CI/CD workflows with multi-stage pipelines
• Gate orchestration, aggregation, and notification systems
• Manual approval workflows and exception management

Progress on Issue #750:

• Milestone 3: 4/5 complete (Security Gates added)
• Remaining: Container Security (final skill)

[cloudflare-workers-and-pages]

Deploying devops-daily with    Cloudflare Pages

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