- new internal/sysadmin package (overview/kb/features/settings) with small
port interfaces; business packages stay unaware of sysadmin
- new routes /api/v1/admin/system/{overview,kb,features,settings} guarded
by requireSystemAdmin
- goose 00049: system_settings table (key/jsonb value, updated_by/at)
- SettingSpec whitelist registry with DB > env > default precedence
- register sysadmin in module-boundaries.yaml (archtest rules)