fix: 修复暗黑模式样式兼容性

- 在 tailwind.config.js 中启用 darkMode: 'class' 并扩展语义化颜色变量
- 将全项目硬编码颜色（bg-white、text-gray-*、border-gray-* 等）替换为语义化类名
- 修复 popup/index.html 硬编码浅色背景色
- 同步更新相关单元测试中的类名断言

components/SwitchButtonGroup.tsx

@@ -28,7 +28,7 @@ export default function SwitchButtonGroup<T extends string | number = string>({
 
   return (
     <div
-      className="w-full mb-4 rounded-xl border border-gray-200 bg-gray-50 p-1.5 flex gap-1"
+      className="w-full mb-4 rounded-xl border border-border bg-muted p-1.5 flex gap-1"
       style={sx}
     >
       {options.map((option) => (
@@ -40,8 +40,8 @@ export default function SwitchButtonGroup<T extends string | number = string>({
             sizeClasses[size]
           } ${
             value === option.value
-              ? 'bg-white text-blue-600 shadow-sm'
-              : 'text-gray-500 hover:text-gray-700 hover:bg-white/50'
+              ? 'bg-background text-primary shadow-sm'
+              : 'text-muted-foreground hover:text-foreground hover:bg-background/50'
           }`}
           style={buttonSx}
         >