Replace the Pure Ink light/dark/comic theme system with the CYBER
single-theme dark palette from the reviewed prototype: OKLCH surfaces,
one neon-cyan accent, and monospace-first typography.
Arco components were reading colors from arco.css because no
ConfigProvider was mounted, so the theme values in arco-theme.ts never
took effect. Bridge CYBER into Arco through its --color-* variables in
global.scss instead, and align arco-theme.ts to match.
Brightness and style switches are gone: useTheme now pins dark, the
comic font faces and locale keys are removed, and ThemeSwitch.vue is
deleted along with its sidebar slot and display setting.