Publish a documentation site via GitLab Pages (MkDocs)

Problem/Motivation

The documentation lives in the GitLab wiki as a single long page. The shared gitlab_templates CI already includes a pages job that publishes an MkDocs site at project.pages.drupalcode.org/ai_metering once mkdocs.yml and docs/index.md exist on the default branch.

Proposed resolution

Add mkdocs.yml and split the wiki content into per-topic pages under docs/

AI assistance

Yes.