Update scripts/docs to write directly into showcase/shell-docs/src/content/reference/
(consumed by /reference/[...slug]) instead of the legacy docs/content/docs tree.
Adds repo-root cwd anchoring, mkdir -p on the destination, allSettled so a single
missing source doesn't abort the run; generates 25 MDX pages (20 V1 + 5 SDK) and
shell-docs build passes.