- Require `--site-name` when generating mkdocs.yml to ensure valid configs
- Inject site_name explicitly into generated mkdocs.yml
- Echo MkDocs serve URL (http://127.0.0.1:8000) before starting server
- Fix MkDocs nav emission to correctly resolve docs-relative paths
- Align MkDocs-related optional dependencies with a compatible, pinned set
These changes make MkDocs generation valid by default, improve UX when serving,
and prevent nav path and plugin compatibility issues.
