Function render_reference_markdown 

pub fn render_reference_markdown() -> String

Render the reference page for built-in type constructors, enums, and interfaces.

The output is a self-contained markdown page generated from the registries in this crate. It is the source of truth for the checked-in reference page at docs/generated/builtins-reference.md; make check-builtins-docs runs it and fails CI if the committed file differs from the generated output.