fix: PC 端全站移动端响应式修复

Critical:
- header.tsx: 手机菜单按钮 flex-row→flex-col, 修复 w-full 溢出
- compare/page.tsx: 参数面板 grid-cols-3→grid-cols-1 sm:grid-cols-3

High:
- sandbox/page.tsx: header 区 flex-wrap + 模型选择器 w-48→w-40 sm:w-48
- member/page.tsx: 功能对比行 grid 布局替代 flex, 防溢出
- workshop/page.tsx: 编辑区 flex-col sm:flex-row + 按钮组 flex-wrap

Medium:
- analytics/page.tsx: domain name truncate
- skills/[id]: CTA 按钮 w-full sm:w-auto

frontend/src/app/sandbox/page.tsx

@@ -289,8 +289,8 @@ function SandboxPage() {
             <p className="text-sm text-muted-foreground mt-0.5">{t.sandbox.subtitle}</p>
           </div>
         </div>
-        <div className="flex items-center gap-3">
-          <ModelSelector value={model} onChange={setModel} className="w-48" />
+        <div className="flex flex-wrap items-center gap-2 sm:gap-3">
+          <ModelSelector value={model} onChange={setModel} className="w-40 sm:w-48" />
           {!isLoggedIn && (
             <Link href="/auth"
               className="px-4 py-1.5 text-sm font-medium text-brand-600 border border-brand-200 rounded-lg hover:bg-brand-50">