argus flagged (approving) that an unvalidated label could build a path
outside the state dir; mara called it out as a usability issue in its
own right, not just a low-risk security nit — a typo'd label should
give a precise 'not a valid label' error, not a confusing file-not-found
or an unexpected traversal.
Reject anything outside the plain lowercase+digits+hyphens charset
dashboard/extra_forges.rs already enforces on write, before touching
the filesystem at all.
46bdb78466