重构前端：临床仪表盘主题 + AI日报编辑版式

- 全面采用临床数据仪表盘风格：IBM Plex Mono/Sans、teal 主色、无阴影设计
- theme.css 完整重写设计 token，支持亮色/暗色/跟随系统三挡切换
- ThemeControls 简化为图标三键切换组件
- NewsCard 临床风格重排：ALL CAPS 分类标签、INSIGHT 观点块
- NewsReader 精选栏：时间轴布局，蓝点 + 垂直轨道线
- AI日报全新排版：左侧 ARCHIVE 侧边栏 + 主区编辑版式
  - 报头：中文数字日期、星期、PHARMA INTEL tagline
  - 分节：52px teal 编号 + 22px 中文分类 + 英文副标题
  - 内容卡片：圆角12px，teal 标题，chips 行（来源/时间/评分）
  - 页脚统计：STORIES / PROCESSED / SOURCES
- 全响应式：≤900px 平板、≤640px 移动端自适应

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/App.vue

@@ -1,3 +1,49 @@
 <template>
-  <router-view />
+  <router-view v-slot="{ Component }">
+    <component
+      :is="Component"
+      :theme-mode="themeMode"
+      :resolved-theme="resolvedTheme"
+      @set-theme-mode="setThemeMode"
+    />
+  </router-view>
 </template>
+
+<script setup>
+import { onMounted, onUnmounted, ref, watch } from 'vue'
+
+const STORAGE_KEY = 'theme-mode'
+const themeMode = ref(localStorage.getItem(STORAGE_KEY) || 'system')
+const resolvedTheme = ref('light')
+let mediaQuery
+
+function getSystemTheme() {
+  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
+}
+
+function applyTheme() {
+  const nextTheme = themeMode.value === 'system' ? getSystemTheme() : themeMode.value
+  resolvedTheme.value = nextTheme
+  document.documentElement.dataset.theme = nextTheme
+  document.documentElement.style.colorScheme = nextTheme
+}
+
+function setThemeMode(mode) {
+  themeMode.value = mode
+}
+
+watch(themeMode, (mode) => {
+  localStorage.setItem(STORAGE_KEY, mode)
+  applyTheme()
+})
+
+onMounted(() => {
+  mediaQuery = window.matchMedia('(prefers-color-scheme: dark)')
+  mediaQuery.addEventListener('change', applyTheme)
+  applyTheme()
+})
+
+onUnmounted(() => {
+  mediaQuery?.removeEventListener('change', applyTheme)
+})
+</script>