Add MkDocs Source Links

[filipchristiansen]

What kind of change does this PR introduce?

• Add a project
• Update a project
• Remove a project
• Add or update a category
• Change configuration
• Documentation
• Other, please describe:

Description:

Adds MkDocs Source Links (pypi: mkdocs-source-links, plugin name source-links, category links-refs).

MkDocs plugin that rewrites parent-directory (](../path)) markdown links to your git forge's view URLs in the built HTML only. Source markdown keeps working relative paths (so links still resolve on the forge and in your IDE); files become blob URLs and directories tree URLs, with the branch resolved from config / edit_uri. Supports GitHub (incl. Enterprise), GitLab, Bitbucket, Gitea/Forgejo (incl. Codeberg), and Azure DevOps, with host autodetection and an explicit forge override. Docs: https://filipchristiansen.github.io/mkdocs-source-links/

Checklist:

• I have read the CONTRIBUTING guidelines.
• I have not modified the README.md file. Projects are only supposed to be added or updated within the projects.yaml file since the README.md file is automatically generated.

[filipchristiansen]

The failing check_projects.py run is unrelated to this PR. The only error is for the Zettelkasten project, whose upstream package no longer exposes the [mkdocs.themes] zettelkasten-solarized-light entry point recorded in the catalog:

Zettelkasten:
     Missing entry point [mkdocs.themes] 'zettelkasten-solarized-light'.
     Instead got {'mkdocs.plugins': ['zettelkasten'], 'mkdocs.themes': ['zettelkasten']}

Since check_projects.py validates every project and fails the whole run if any one is broken, this pre-existing mismatch would fail on main and any open PR.

This PR's entry validates cleanly — installing mkdocs-source-links shows the expected entry point:

[mkdocs.plugins]
source-links = mkdocs_source_links.plugin:SourceLinksPlugin

Only projects.yaml was modified (one project added); README.md is untouched. Happy to rebase once the unrelated Zettelkasten entry is sorted out.