New lib/tests/toggle-external-repo-resolution.test.sh: sandbox
replicating the real ~/.claude/lib -> <repo>/lib symlink layout,
invokes toggle-external.sh THROUGH the symlinked path and asks
`status emil-design-eng` (marked enabled in the physical repo tree).
Demonstrates J4-20 (UNTESTABLE + latent bug) against the CURRENT code,
on purpose — this commit is RED: reports "missing" instead of
"enabled", because toggle-external.sh:34's logical `cd` (no -P)
resolves REPO to the symlink's logical parent instead of the physical
repo root, so SKILLS_DIR/DISABLED_DIR point at the wrong tree. Same
BLK-006 bug class as profile.sh's historical breaks, un-ported here —
latent today (no in-repo caller hits direct `~/.claude/lib/...`
invocation), but reachable.
This intentionally reds `make test`. Next commit fixes it.
