docs(rfc): support bundled subdirectory templates in @org/create

Let manifest entries use relative paths (`./templates/demo`) that resolve
against the enclosing @org/create package root, so orgs can ship one
package containing N templates instead of publishing N @org/template-*
packages — the pattern already used by create-vite, create-next-app, and
most enterprise scaffolding kits.

Vite+ fetches the tarball URL already returned by the registry manifest,
extracts it once per version into `$VP_HOME/tmp/create-org/<scope>/<name>/<version>/`,
and scaffolds by directory copy. Paths that escape the package root are
rejected at schema-validation time.

Addresses @fengmk2's review feedback on #1398 asking whether
`./templates/demo`-style bundled paths would be supported.

Author: fengmk2