pub fn code_description_for(code: &str) -> Option<CodeDescription>Expand description
W2.3 / 1.17 — build a CodeDescription for a Shape error code string.
Returns None if code is empty (defensive; every Shape error code
is non-empty in practice). URL fragment is the code — e.g. E0100 →
https://book.shape-lang.dev/appendix/error-codes/#E0100.
Exposed via the module’s public surface so the borrow/MIR diagnostic path and the per-validator diagnostics share one URL builder.