feat(api): derive ascii structure names for documents

Build each document's structure name in a single pass from its owner,
category, section, and field, joining display parts with an em dash
and slug parts with dashes so Persian text never leaks into slugs or
download filenames. Expose structure_name_slug on document payloads
and map documentable entities to their section registries via config
so the locator can resolve labels per domain. Personal info gains
explicit page field-key slugs.