feat(compose): support subdirectory globs in composed_model sources
Globs like `grids/*.json` now work: the validator allows `/`, and the
symlink loop preserves the relative path (mkdir -p parent dirs, symlink
target uses $csnap/$rel) instead of flattening via `basename`.
Also fixes a latent shq-in-double-quotes bug: {host_q} was wrapped in
`"..."`, making shq's single-quote wrapping literal characters in the
path — every ln/dirname call failed silently, producing zero symlinks.
{host_q} is now bare with only "$rel" quoted.
Tested on live cluster with test-composed recipe (grids/*.json source):
grids/ subdir created with 75 L*.json symlinks resolving correctly
inside the container.