Stage 1 of the page builder: Pages schema with 14 valid slugs,
BlockTypes registry (26 block types with settings schemas and data
loaders), Defaults module matching existing templates, ETS-backed
PageCache GenServer, and Pages context (get_page/save_page/reset_page
with cache -> DB -> defaults lookup). 34 tests, zero visual change.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
