v0.122.0

Scaffold creates the experiments/ and screenshots/ scratch directories, and every repository walk prunes them.

Context

A project needs a declared place to put a throwaway file -- a prototype, a
produced repository, a capture, a mid-work screenshot -- so that nothing has to
reach for a system temporary directory. Scaffold now creates two such
directories at the project root, experiments/ and screenshots/, each carrying a
committed .gitignore holding '*' and '!.gitignore'. That spelling is what makes
the directory exist in a fresh clone, so tooling may rely on it being there,
while nothing inside it can be committed by accident; a line in the root
.gitignore would leave the directory absent after a clone instead.

Both files are ordinary shared (target-independent) scaffold mappings, so
re-running scaffold over a project whose scratch directories already hold work
merges to a no-op and touches nothing inside them.

rlsbl's repository walks read the filesystem rather than git's index, so the
ignore file alone would not keep them out: a throwaway git repository under
experiments/ could turn dead-module detection or the unregistered-project scan
red. Every walk now prunes both names at the root of the project it is walking,
from one authority (rlsbl.scratch_dirs). The pruning is root-scoped, matching
where scaffold creates them, so a directory of the same name nested deeper
inside a project is still an ordinary source directory.

Features

• Scratch directories. rlsbl scaffold now creates experiments/ and screenshots/ at the project root, each carrying a committed .gitignore that keeps the directory present in a fresh clone while ignoring everything inside it. Every rlsbl check that walks the project tree prunes both at the project root, so a throwaway probe, a produced repository, or a screenshot left in one of them cannot turn a check red.