Data vs presentation

Architecture facts live in data/; the book's look lives in wdoc/ templates. Fix each in its own place.

A WAD keeps content and rendering strictly apart: data/ holds block instances, wdoc/book/ holds projections over the gathered lists. Consequences: a wrong fact is fixed in data (never by editing a page); a layout problem is fixed in a template (never by contorting data); and wcl check wad.wcl validates the model regardless of how it renders.

The templates derive everything — context and container diagrams from relation roll-ups, the ER diagram from domain_object fields, pipelines from stage DAGs — so data stays the single source of truth.