docs(11): Add CI/CD quick guide page in docs

[Jouzep]

Description

Adds comprehensive CI/CD quick guide documentation explaining the GitHub Actions pipeline, test stages, deployment workflow, and how to debug issues.

Changes

• ✅ Document what runs when (PR, push to main, tags)
• ✅ Explain all test types (lint, unit, integration, golden)
• ✅ Show how to read CI results and GitHub Actions dashboard
• ✅ Provide clear troubleshooting guide
• ✅ Document deployment workflow (staging → production)
• ✅ Show how to create releases
• ✅ Include performance metrics and optimization
• ✅ Add branch protection rules explanation
• ✅ Provide best practices
• ✅ Add failure examples and solutions

Closes

• [Docs] CI/CD quick page in wiki #11 - [Docs] CI/CD quick page in docs

Files Changed

• docs/CI_CD_GUIDE.md - New comprehensive CI/CD guide

Content Overview

• Overview: CI/CD pipeline explanation
• What Runs When: Visual diagrams for different triggers
• Test Types: Detailed breakdown of all 4 test tiers
• Reading Results: How to check GitHub Actions dashboard
• Fixing Failures: Step-by-step solutions for each failure type
• Deployment: Staging and production workflow
• Releases: How to create tagged releases
• Troubleshooting: Common issues and solutions
• Best Practices: Recommendations for developers

Length

• ~400 lines (detailed but readable)
• Can be read in 15-20 minutes
• Heavy use of examples and diagrams