feat(web): extract hardcoded CSS into design token system (ATB-52) (#85)
* docs: ATB-52 CSS token extraction design doc
* docs: ATB-52 implementation plan
* test(web): add failing preset completeness tests (ATB-52)
* test(web): improve preset test descriptions (ATB-52)
* feat(web): add neobrutal-light and neobrutal-dark JSON presets with font-size-xs token (ATB-52)
* feat(web): switch base layout to JSON preset import, remove TS preset (ATB-52)
* fix(web): replace all hardcoded CSS values with design tokens in mod and structure UI (ATB-52)