feat(theme): 添加主题切换功能- 新增 ThemeToggle 组件，用于在界面上显示主题切换按钮

- 实现 useTheme钩子，提供主题管理逻辑- 添加暗黑模式和亮色模式的切换支持
- 实现本地存储和系统主题的自动检测
- 添加主题切换时的事件广播

src/components/ThemeToggle.vue

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+<template>
+  <n-button 
+    circle 
+    size="medium" 
+    class="theme-toggle"
+    @click="toggleTheme"
+  >
+    <template #icon>
+      <n-icon v-if="isDark">
+        <Sunny />
+      </n-icon>
+      <n-icon v-else>
+        <Moon />
+      </n-icon>
+    </template>
+  </n-button>
+</template>
+
+<script setup>
+import { Moon, Sunny } from '@vicons/ionicons5'
+import { useTheme } from '@/composables/useTheme'
+
+const { isDark, toggleTheme } = useTheme()
+</script>
+
+<style scoped lang="scss">
+.theme-toggle {
+  transition: all 0.3s ease;
+  
+  &:hover {
+    transform: scale(1.1);
+  }
+}</style>

src/composables/useTheme.js

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+import { ref, onMounted, onUnmounted } from 'vue'
+
+// 全局响应式主题状态
+const isDark = ref(false)
+
+// 检查当前主题状态
+const checkCurrentTheme = () => {
+  return document.documentElement.classList.contains('dark') || 
+         document.documentElement.getAttribute('data-theme') === 'dark'
+}
+
+// 更新响应式状态
+const updateReactiveState = () => {
+  isDark.value = checkCurrentTheme()
+}
+
+// 主题管理逻辑
+export function useTheme() {
+  let mutationObserver = null
+  
+  // 初始化主题
+  const initTheme = () => {
+    const savedTheme = localStorage.getItem('theme')
+    const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches
+    
+    if (savedTheme === 'dark' || (!savedTheme && prefersDark)) {
+      setDarkTheme()
+    } else {
+      setLightTheme()
+    }
+    
+    // 立即更新响应式状态
+    updateReactiveState()
+  }
+  
+  // 设置深色主题
+  const setDarkTheme = () => {
+    document.documentElement.classList.add('dark')
+    document.documentElement.setAttribute('data-theme', 'dark')
+    document.body.classList.add('dark')
+    document.body.setAttribute('data-theme', 'dark')
+    localStorage.setItem('theme', 'dark')
+    
+    // 立即更新响应式状态
+    isDark.value = true
+    
+    // 触发主题更新事件
+    window.dispatchEvent(new CustomEvent('theme-change', { detail: { isDark: true } }))
+  }
+  
+  // 设置浅色主题
+  const setLightTheme = () => {
+    document.documentElement.classList.remove('dark')
+    document.documentElement.removeAttribute('data-theme')
+    document.body.classList.remove('dark')
+    document.body.removeAttribute('data-theme')
+    localStorage.setItem('theme', 'light')
+    
+    // 立即更新响应式状态
+    isDark.value = false
+    
+    // 触发主题更新事件
+    window.dispatchEvent(new CustomEvent('theme-change', { detail: { isDark: false } }))
+  }
+  
+  // 切换主题
+  const toggleTheme = () => {
+    if (isDark.value) {
+      setLightTheme()
+    } else {
+      setDarkTheme()
+    }
+  }
+  
+  // 监听系统主题变化
+  const setupSystemThemeListener = () => {
+    const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)')
+    mediaQuery.addListener(() => {
+      const savedTheme = localStorage.getItem('theme')
+      // 只有在用户没有手动设置主题时才跟随系统
+      if (!savedTheme) {
+        initTheme()
+      }
+    })
+  }
+  
+  // 设置DOM变化监听器（确保响应式状态同步）
+  const setupDOMObserver = () => {
+    if (typeof window !== 'undefined') {
+      mutationObserver = new MutationObserver(() => {
+        updateReactiveState()
+      })
+      
+      // 监听documentElement和body的变化
+      mutationObserver.observe(document.documentElement, {
+        attributes: true,
+        attributeFilter: ['class', 'data-theme']
+      })
+      
+      mutationObserver.observe(document.body, {
+        attributes: true,
+        attributeFilter: ['class', 'data-theme']
+      })
+    }
+  }
+  
+  // 清理监听器
+  const cleanup = () => {
+    if (mutationObserver) {
+      mutationObserver.disconnect()
+      mutationObserver = null
+    }
+  }
+  
+  // 获取当前主题
+  const getCurrentTheme = () => {
+    return isDark.value ? 'dark' : 'light'
+  }
+  
+  // 组件挂载时初始化
+  onMounted(() => {
+    setupDOMObserver()
+    updateReactiveState()
+  })
+  
+  // 组件卸载时清理
+  onUnmounted(() => {
+    cleanup()
+  })
+  
+  return {
+    isDark,
+    initTheme,
+    toggleTheme,
+    setDarkTheme,
+    setLightTheme,
+    setupSystemThemeListener,
+    getCurrentTheme,
+    updateReactiveState
+  }
+}