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/components/hermes/settings/DisplaySettings.vue

@@ -3,7 +3,6 @@ import { computed } from 'vue'
 import { useMessage } from '@/composables/useMessage'
 import { useI18n } from 'vue-i18n'
 import { useSettingsStore } from '@/stores/hermes/settings'
-import { useTheme, type BrightnessMode } from '@/composables/useTheme'
 import { requestCompletionNotificationPermission, showCompletionNotification, type CompletionNotificationPermissionResult } from '@/utils/completion-notification'
 import { clampChatInputHeight, MAX_CHAT_INPUT_HEIGHT, MIN_CHAT_INPUT_HEIGHT } from '@/utils/chat-input-height'
 import SettingRow from './SettingRow.vue'
@@ -11,13 +10,7 @@ import SettingRow from './SettingRow.vue'
 const settingsStore = useSettingsStore()
 const message = useMessage()
 const { t } = useI18n()
-const { brightness, setBrightness } = useTheme()
 
-const themeOptions = [
-  { label: t('settings.display.themeLight'), value: 'light' },
-  { label: t('settings.display.themeDark'), value: 'dark' },
-  { label: t('settings.display.themeSystem'), value: 'system' },
-]
 const chatInputHeight = computed(() => clampChatInputHeight(settingsStore.display.chat_input_height))
 
 async function save(values: Record<string, any>) {
@@ -29,12 +22,6 @@ async function save(values: Record<string, any>) {
   }
 }
 
-function handleThemeChange(val: string) {
-  const m = val as BrightnessMode
-  setBrightness(m)
-  save({ skin: m })
-}
-
 function handleChatInputHeightChange(value: number | null) {
   return save({ chat_input_height: clampChatInputHeight(value) })
 }
@@ -90,9 +77,6 @@ async function testCompletionNotification() {
 
 <template>
   <section class="settings-section">
-    <SettingRow :label="t('settings.display.theme')" :hint="t('settings.display.themeHint')">
-      <a-select :model-value="brightness" :options="themeOptions" size="small" class="input-sm" @update:model-value="v => handleThemeChange(String(v))" />
-    </SettingRow>
     <SettingRow :label="t('settings.display.streaming')" :hint="t('settings.display.streamingHint')">
       <a-switch :model-value="settingsStore.display.streaming" @update:model-value="v => save({ streaming: v })" />
     </SettingRow>