fix(setup): default bare disable to local scope, add --local flag

Bare entire disable had started resolving via settingsTargetFile (project-first), so on a configured repo it flipped the committed, team-shared settings.json instead of the personal settings.local.json. Because local overrides project in the merged view, disable only needs the local override to take effect, and touching the committed file is a scope regression with no way to opt out.

Restore origin/main's default (bare disable -> settings.local.json), add an explicit --local flag for symmetry with enable, validate that --local/--project aren't combined, and print which settings file was changed. Enable stays asymmetric on purpose: it must reach the committed file to recover a repo disabled there (#1140), so it keeps resolving via settingsTargetFile.