Introduces a frozen Set<string> of directory basenames (node_modules, .git,
dist, build, .next, .sisyphus, .omx, .turbo, coverage, out, .cache,
.vscode-test, target, .local-ignore) that callers performing recursive
filesystem scans should skip.
This is shared infrastructure for upcoming fixes in rules-injector,
command-discovery, and claude-code-command-loader that currently descend
into node_modules and other junk directories, causing slow plugin init
and slow edit loops when the plugin is launched in-tree.
Sisyphus