Address review findings on the #2923 fail-closed parse fix:
- Comment-only files produce ValueExpected with no JSON value; treat that
as empty config instead of INVALID_JSONC. Partial object trees still throw.
- readConfigLayers no longer lets one unparseable layer abort valid sibling
layers. Mutations still fail closed on the custom/user write target.
Co-authored-by: serkraser <serkraser@gmail.com>