Function render_syntax_reference 

pub fn render_syntax_reference() -> String

Render the Syntax concept as a standalone reference document.

This is the single source for content/en/syntax.md (which is a committed, drift-tested mirror) and for help syntax. Each Syntax fragment becomes a ## <title> section, in registry order. LANGUAGE.md stays hand-authored as the deeper human reference; a test guards that it still covers this surface.