manifest.yaml gains system_templates + page_templates declarations; each page
template's .ninjatpl source lives at templates/<system>/<key>.ninjatpl and is
validated at pack time. Verify no longer rejects declared system/page
templates on codeless manifests (guest template_keys stay rejected) — the cms
host registers them source-tracked and renders the files through the same
host pongo pipeline powered blocks use. Blog/system/normal page layouts are
now fully expressible with zero code.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
