docs: document draft MR CI skipping

What does this MR do and why?

This tells agents to add [skip ci] to Draft MR titles while iterating, avoiding unnecessary MR pipelines similar to gitlab-org/gitlab!257831 (merged). It also explains how to start CI when the MR is ready.

Related Issues

Testing

Targeted Markdownlint, Vale, and Lychee checks pass. mise lint:docs reaches pre-existing broken local links to generated documentation files.

Performance Analysis

• This merge request does not introduce any performance regression. If a performance regression is expected, explain why.

Agent context: long-form analysis, file-by-file walkthroughs, profiler output, alternatives considered

The guidance is byte-identical in AGENTS.md and CLAUDE.md. This project creates MR pipelines for feature branches, but not branch pipelines, so the MR title is the relevant skip mechanism. The trailing marker keeps the title's Conventional Commits prefix intact.