adopt CYBER neon-dark theme tokens

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.

packages/client/src/composables/useTheme.ts

@@ -1,91 +1,28 @@
-import { ref, watch, computed } from 'vue'
+import { ref, computed } from 'vue'
 
-export type BrightnessMode = 'light' | 'dark' | 'system'
-export type ThemeStyle = 'ink' | 'comic'
+// CYBER 是单色暗色主题：亮度与风格切换器已移除（comic 与 light 主题不再提供）。
+// 这里保留 isDark 以兼容 App.vue / JourneyView 里的 :class 绑定，值恒为 true。
+const isDark = ref(true)
 
-const BRIGHTNESS_KEY = 'hermes_brightness'
-const STYLE_KEY = 'hermes_style'
+export type BrightnessMode = 'dark'
 
-const brightness = ref<BrightnessMode>(
-  (localStorage.getItem(BRIGHTNESS_KEY) as BrightnessMode) || 'system',
-)
+const brightness = ref<BrightnessMode>('dark')
 
-const style = ref<ThemeStyle>(
-  (localStorage.getItem(STYLE_KEY) as ThemeStyle) || 'ink',
-)
-
-const isDark = ref(false)
-const isComic = ref(false)
-
-function resolveDark(b: BrightnessMode): boolean {
-  if (b === 'system') {
-    return window.matchMedia('(prefers-color-scheme: dark)').matches
-  }
-  return b === 'dark'
-}
-
-function applyClasses() {
-  const dark = resolveDark(brightness.value)
-  isDark.value = dark
-  isComic.value = style.value === 'comic'
-  document.documentElement.classList.toggle('dark', dark)
-  document.documentElement.classList.toggle('comic', isComic.value)
-  // Arco Design dark theme mechanism (Phase 005)
-  document.documentElement.setAttribute('arco-theme', dark ? 'dark' : 'light')
-}
-
-// Initial
-applyClasses()
-
-// Listen for system preference changes
-window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
-  if (brightness.value === 'system') {
-    applyClasses()
-  }
-})
-
-// Persist & apply on change
-watch(brightness, (b) => {
-  localStorage.setItem(BRIGHTNESS_KEY, b)
-  applyClasses()
-})
-
-watch(style, (s) => {
-  localStorage.setItem(STYLE_KEY, s)
-  applyClasses()
-})
+// 固定应用暗色：Arco 的 token 通过 arco-theme 属性切换，项目的令牌写在 :root。
+document.documentElement.setAttribute('arco-theme', 'dark')
 
 export function useTheme() {
-  const themeName = computed(() => {
-    const b = isDark.value ? 'dark' : 'light'
-    return isComic.value ? `comic-${b}` : b
-  })
+  const themeName = computed(() => 'dark')
 
-  function setBrightness(b: BrightnessMode) {
-    brightness.value = b
-  }
-
-  function setStyle(s: ThemeStyle) {
-    style.value = s
-  }
-
-  function toggleBrightness() {
-    brightness.value = isDark.value ? 'light' : 'dark'
-  }
-
-  function toggleStyle() {
-    style.value = isComic.value ? 'ink' : 'comic'
+  function setBrightness(_b: BrightnessMode) {
+    // 单主题：忽略任何切换请求。
+    brightness.value = 'dark'
   }
 
   return {
     brightness,
-    style,
     isDark,
-    isComic,
     themeName,
     setBrightness,
-    setStyle,
-    toggleBrightness,
-    toggleStyle,
   }
 }