Add Comprehensive CI/CD Documentation in ci_guide.md

[RickyDicaprio]

The CI folder contains formatting, linting, and test scripts, but the documentation needs to clearly explain how contributors should use them.

Tasks

1. Update docs/ci_guide.md with step-by-step explanations
2. Explain what format.sh, lint.sh, and run_tests.sh do
3. Add instructions to run CI checks locally
4. Add a diagram showing the CI workflow
5. Link CI checks to .github/workflows/main-ci.yml

Goal
Help contributors understand the CI process so they can test their work before creating pull requests.