feat(web): 官网移动端适配

- 导航栏：≤768 隐藏横向链接，显示汉堡按钮；点击展开下拉菜单，含全部链接和 CTA
- 新增 ≤600 手机断点：footer 单列、grid 单列、container 内边距收窄、标题字号下调
- 首页：≤768 隐藏 Hero mock 预览（装饰性），≤600 CTA 按钮纵向排列
- features 页（库存/审批）：hamburger 导航、≤768 隐藏 composite 视觉、≤600 footer 单列
- 文档页（docs.css）：≤600 表格横向可滚
- 下载页：≤600 平台卡片单列排列

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

web/assets/nav.js

@@ -23,16 +23,35 @@
     if (el) el.classList.toggle('open');
   }
 
-  // 点击外部关闭 dropdown
-  document.addEventListener('click', function(e) {
-    var menu = document.getElementById('userDropdown');
+  function toggleMobileMenu() {
+    var menu = document.getElementById('nav-mobile-menu');
+    var btn  = document.getElementById('nav-hamburger');
     if (!menu) return;
-    var navUser = menu.closest('.nav-user');
-    if (navUser && !navUser.contains(e.target)) menu.classList.remove('open');
+    var isOpen = menu.classList.toggle('open');
+    if (btn) btn.setAttribute('aria-expanded', isOpen ? 'true' : 'false');
+  }
+
+  // 点击外部关闭 dropdown 和 mobile menu
+  document.addEventListener('click', function(e) {
+    var userMenu = document.getElementById('userDropdown');
+    if (userMenu) {
+      var navUser = userMenu.closest('.nav-user');
+      if (navUser && !navUser.contains(e.target)) userMenu.classList.remove('open');
+    }
+    var mobileMenu = document.getElementById('nav-mobile-menu');
+    var hamburger  = document.getElementById('nav-hamburger');
+    if (mobileMenu && hamburger) {
+      var topnav = mobileMenu.closest('nav');
+      if (topnav && !topnav.contains(e.target)) {
+        mobileMenu.classList.remove('open');
+        hamburger.setAttribute('aria-expanded', 'false');
+      }
+    }
   });
 
   function renderNav() {
     var cta = document.getElementById('nav-cta');
+    var mobileCta = document.getElementById('nav-mobile-cta');
     if (!cta) return;
     var user = getAuthUser();
     if (user) {
@@ -58,22 +77,47 @@
         +   '<div class="nav-dropdown-divider"></div>'
         +   '<button class="logout" onclick="doLogout()"><i data-lucide="log-out" class="icon"></i>退出登录</button>'
         + '</div></div>';
+      if (mobileCta) {
+        mobileCta.innerHTML =
+          '<a href="/app/" class="btn btn-ghost">进入管理端</a>'
+          + '<button class="btn btn-ghost" onclick="doLogout()">退出登录</button>';
+      }
     } else {
       cta.innerHTML =
         '<a href="/app/" class="btn btn-ghost">登录</a>'
         + '<a href="/app/" class="btn btn-primary">免费试用</a>';
+      if (mobileCta) {
+        mobileCta.innerHTML =
+          '<a href="/app/" class="btn btn-ghost">登录</a>'
+          + '<a href="/register/" class="btn btn-primary">注册门店</a>';
+      }
     }
     if (window.lucide) lucide.createIcons();
   }
 
   // 暴露给 onclick 调用
-  window.toggleUserMenu = toggleUserMenu;
+  window.toggleUserMenu  = toggleUserMenu;
+  window.toggleMobileMenu = toggleMobileMenu;
   window.doLogout = doLogout;
 
   document.addEventListener('DOMContentLoaded', function() {
     renderNav();
     if (window.lucide) lucide.createIcons();
 
+    var hamburger = document.getElementById('nav-hamburger');
+    if (hamburger) hamburger.addEventListener('click', toggleMobileMenu);
+
+    // 点击 mobile menu 链接后自动收起
+    var mobileMenu = document.getElementById('nav-mobile-menu');
+    if (mobileMenu) {
+      mobileMenu.querySelectorAll('a').forEach(function(a) {
+        a.addEventListener('click', function() {
+          mobileMenu.classList.remove('open');
+          if (hamburger) hamburger.setAttribute('aria-expanded', 'false');
+        });
+      });
+    }
+
     // 页内锚点平滑滚动
     document.querySelectorAll('a[href^="#"]').forEach(function(a) {
       a.addEventListener('click', function(e) {