fix(document): improve mobile sidebar style and UX (#6464)

* fix(document): improve mobile sidebar style and UX

- Add icons to 6 navigation tabs (BookOpen, Code, Lightbulb, CircleHelp, Scale, History)
- Reduce mobile sidebar padding and separator spacing
- Fix icon container size in RootToggle dropdown (36px → 20px)
- Keep sidebar open when switching between top-level tabs
- Remove top gradient mask on mobile sidebar viewport
- Fix long URL overflow in article content on mobile
- Fix TOC popover trigger text overflow on mobile

* docs: 中国大陆 → 中国大陆版

* docs: 海外版→国际版, 国内版→中国大陆版

---------

Co-authored-by: archer <archer@archerdeMac-mini.local>

document/components/sideBar.tsx

@@ -71,7 +71,7 @@ const CustomFolder: FC<{ item: PageTree.Folder; level: number; children: ReactNo
 };
 
 const CustomSeparator: FC<{ item: PageTree.Separator }> = ({ item }) => (
-  <div className="text-sm font-semibold px-2 py-2 mt-4 mb-2">{item.name}</div>
+  <div className="text-sm font-semibold px-2 py-1.5 mt-1 mb-1 first:mt-0">{item.name}</div>
 );
 
 export const CustomSidebarComponents: SidebarComponents = {

document/components/sidebarKeepOpen.tsx

@@ -0,0 +1,33 @@
+'use client';
+
+import { usePathname } from 'next/navigation';
+import { useRef } from 'react';
+import { useSidebar } from 'fumadocs-ui/provider';
+
+/**
+ * 移动端：点击一级 tab 切换时不关闭 sidebar，点击二级路由时正常关闭。
+ * 
+ * 在渲染阶段检测是否为 tab 间切换，是则设 closeOnRedirect = false。
+ */
+export function SidebarKeepOpen({ tabUrls }: { tabUrls: string[] }) {
+  const pathname = usePathname();
+  const prevPathname = useRef(pathname);
+  const { closeOnRedirect } = useSidebar();
+
+  if (prevPathname.current !== pathname) {
+    const prev = prevPathname.current;
+    prevPathname.current = pathname;
+
+    // 判断是否是 tab 间切换（从一个 tab 根路径跳到另一个 tab 根路径）
+    const prevTab = tabUrls.find((url) => prev.startsWith(url));
+    const currTab = tabUrls.find((url) => pathname.startsWith(url));
+
+    if (prevTab && currTab && prevTab !== currTab) {
+      // 一级 tab 切换 → 不关闭 sidebar
+      closeOnRedirect.current = false;
+    }
+    // 否则（二级路由跳转）→ 保持默认行为（关闭 sidebar）
+  }
+
+  return null;
+}