Canonical structured documentation for Sema's builtins and special forms.
Each builtin/special form is one markdown file (crates/sema-docs/entries/stdlib/<module>/<slug>.md)
with a single YAML frontmatter block (name, params, returns, see_also, ...) followed by
a markdown body that may contain sema example code blocks.
The filename is just a slug; the name field is canonical (so operator names like *, <=,
null? are fine). From this source sema-docs gen produces a single committed JSON index
([builtin_index]) consumed at runtime by the LSP (hover/completion) and the REPL (apropos/doc).
The website is intentionally not generated from this yet.