Page types for the `seoMarkupSchemas` query (both the `pageTypes` input and the serialized `page_type` output). Values mirror the storefront route taxonomy (FDK `AVAILABLE_PAGE_TYPE`), which the resolver maps to the REST page_type with a generic CAPS_UNDERSCORE ⇄ kebab-lowercase transform — e.g. PROFILE_EMAIL → profile-email. The convex SEO schema model's stored values must use the same singular form so output serialization round-trips.