feat: 友链入口迁至站点区并支持左右页脚独立开关

修复左侧栏/页脚开关无法关闭的问题，改为专用设置接口可靠写入。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/Sidebar.tsx

@@ -66,6 +66,8 @@ export default function Sidebar({
   const isAdmin = user?.role === 'admin';
   const { navPages } = useSitePages();
   const { limits } = useForumLimits();
+  const showFriendLinksNav = limits.nav_show_friend_links !== false;
+  const showSiteSection = navPages.length > 0 || showFriendLinksNav;
 
   const keyword = params.get('keyword') || '';
   const menuKey = resolveMenuKey(loc.pathname, activeBoard, keyword);
@@ -135,7 +137,6 @@ export default function Sidebar({
         {feedNavLink('all', buildHomeUrl(0, sort, permalinkOpts), '全部帖子', <Home aria-hidden />, 0)}
         {user && navItem('favorites', '我的收藏', <Star aria-hidden />, () => nav('/favorites'))}
         {navItem('projects', '开源码桶', <FolderGit2 aria-hidden />, () => nav('/projects'))}
-        {navItem('links', '友情链接', <Link2 aria-hidden />, () => nav('/links'))}
       </nav>
 
       {(boardsLoading && boards.length === 0) ? (
@@ -191,10 +192,11 @@ export default function Sidebar({
         </>
       ) : null}
 
-      {(navPages.length > 0) && (
+      {showSiteSection && (
         <>
           <div className="sidebar-section sidebar-section--spaced">站点</div>
           <nav className="sidebar-nav">
+            {showFriendLinksNav && navItem('links', '友情链接', <Link2 aria-hidden />, () => nav('/links'))}
             {navPages.map(p => (
               navItem(`page-${p.slug}`, p.title, <FileText aria-hidden />, () => nav(pagePath(p.slug, limits)))
             ))}

frontend/src/components/SiteFooter.tsx

@@ -34,18 +34,20 @@ export default function SiteFooter() {
         </div>
 
         <nav className="site-footer__nav" aria-label="站点链接">
-          <span className="site-footer__friend">
-            <Link to="/links">友情链接</Link>
-          </span>
-          {footerPages.map(p => (
+          {limits.footer_show_friend_links !== false && (
+            <span className="site-footer__friend">
+              <Link to="/links">友情链接</Link>
+            </span>
+          )}
+          {footerPages.map((p, i) => (
             <span key={p.slug} className="site-footer__friend">
-              <FooterSep />
+              {(limits.footer_show_friend_links !== false || i > 0) && <FooterSep />}
               <Link to={pagePath(p.slug, limits)}>{p.title}</Link>
             </span>
           ))}
           {icp && (
             <>
-              <FooterSep />
+              {(limits.footer_show_friend_links !== false || footerPages.length > 0) && <FooterSep />}
               <a
                 href={icpURL}
                 target="_blank"