docs(guides): add CI.md mapping GitHub workflows to just recipes

[ThodoreBurne-Jonesbj]

Summary

Adds docs/guides/CI.md: a contributor-oriented map between GitHub Actions (especially ci.yml) and local just recipes.

Why

Contributors run just ci locally but CI runs many parallel jobs with different flags (--locked, ci profile, affected tests on PRs). Without a single place to read this, it is easy to assume local recipes match CI exactly or to miss that just ci runs fix (mutating) first.

What’s in the doc

• TL;DR: CI never auto-fixes; difference between check-clippy / test and check-clippy-ci / test-ci / test-affected-ci.
• just ci, just pr, and useful recipes (build-ci, devnet steps, actions::test).
• Overview table for main workflow files and accurate on: notes (e.g. ci.yml push only to main, zepter PRs targeting main, docs-specs-ci + workflow_dispatch).
• ci.yml job ↔ command table and a Gaps section listing what just ci does not cover.
• Pointer to .github/actions/setup and CONTRIBUTING.md.

Scope

Documentation only; no workflow or Justfile changes.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

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