Documentation authoring

Add a function

1. Copy docs/_schema/function-template.md to docs/functions/<function-slug>/index.md.
2. Replace every placeholder.
3. Add screenshots to the adjacent images directory.
4. Use relative image links such as ./images/<function-slug>-01-overview.png.
5. Add new controlled values to docs/_schema/controlled-vocabulary.yml in the same pull request.
6. Run the documentation validation and Docusaurus build before requesting review.

Core rule

Each function has one canonical topic. Engineering applicability is represented by the modules array, not by duplicating the topic under module folders.