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/components/layout/header.tsx

@@ -183,23 +183,23 @@ export function Header() {
                 {item.label}
               </Link>
             ))}
-            <div className="flex gap-3 mt-4">
+            <div className="flex flex-col gap-2 mt-4">
               {isLoggedIn ? (
                 <>
                   <Button className="w-full" size="sm" asChild>
-                    <Link href="/dashboard" className="flex-1" onClick={() => setMobileOpen(false)}>控制台</Link>
+                    <Link href="/dashboard" onClick={() => setMobileOpen(false)}>控制台</Link>
                   </Button>
-                  <Button variant="outline" size="sm" className="flex-1" onClick={() => { logout(); window.location.href = '/'; }}>
+                  <Button variant="outline" size="sm" className="w-full" onClick={() => { logout(); window.location.href = '/'; }}>
                     退出
                   </Button>
                 </>
               ) : (
                 <>
                   <Button variant="outline" className="w-full" size="sm" asChild>
-                    <Link href="/auth" className="flex-1" onClick={() => setMobileOpen(false)}>登录</Link>
+                    <Link href="/auth" onClick={() => setMobileOpen(false)}>登录</Link>
                   </Button>
                   <Button className="w-full" size="sm" asChild>
-                    <Link href="/auth?tab=register" className="flex-1" onClick={() => setMobileOpen(false)}>注册</Link>
+                    <Link href="/auth?tab=register" onClick={() => setMobileOpen(false)}>注册</Link>
                   </Button>
                 </>
               )}