docs: fix storage transformers reference

[andrewcb22]

Summary

• Replace the hand-written #storage-transformers-1 fragment with a Sphinx :ref: target for the storage transformers section.
• Add an explicit label to the Storage transformers section so the reference is stable.
• Replace an ambiguous storage_transformers inline reference with the existing array metadata label.

Closes #382

Validation

• .\.venv\Scripts\sphinx-build -b html docs docs\_build\html -W --keep-going