feat(ci): add Terraform security analysis workflow with Docker + Gemini integration

[wellingtoong]

🚀 Overview

This PR introduces a GitHub Actions workflow to automatically:

• Run Terraform init, validate and plan
• Convert the plan output to JSON format
• Execute the Cloud Security Analyzer via Docker
• Generate a structured HTML security report
• Upload artifacts (plan.json + HTML report)

The workflow is designed to support infrastructure security analysis before applying changes.

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🔍 What This Adds

• New workflow: .github/workflows/terraform-security-analysis.yml
• Manual execution via workflow_dispatch
• Terraform plan exported as JSON
• Docker-based execution of the Cloud Security Analyzer
• Gemini-powered vulnerability analysis
• HTML report artifact generation

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🧠 Purpose

This enables infrastructure security validation as part of the CI process, supporting:

• Shift-left security practices
• Terraform plan inspection before apply
• Automated vulnerability detection
• Standardized reporting format

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🔐 Security Considerations

• Uses GEMINI_API_KEY from GitHub Secrets
• No AWS credentials required (local plan analysis only)
• Read-only repository permissions

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🧪 How to Run

1. Go to Actions
2. Select Terraform + Cloud Security Analyzer
3. Click Run workflow
4. Provide the Terraform directory input

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📦 Output

The workflow generates:

• terraform-plan-json artifact
• terraform-security-report-html artifact