polish(frontend): 修正中文字重发虚，并疏朗首页与数据区

补齐 Noto 600/800 并关闭伪粗；Header 加大加粗导航并加板块入口；去掉灰块底、加大列表行距，站点数据格居中缩小数字。

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

frontend/components/Header.tsx

@@ -20,6 +20,7 @@ import {
   ChevronDown,
   ShieldCheck,
   MessageSquare,
+  LayoutGrid,
 } from "lucide-react";
 import { apiLogout, apiMe, apiChatUnreadSummary, type User } from "@/lib/api";
 import { hasAuthCookieHint } from "@/lib/cookies";
@@ -233,14 +234,21 @@ export default function Header({
               </span>
             </span>
           </Link>
-          <nav className="hidden lg:flex items-center gap-1 pl-3" style={{ borderLeft: "1px solid var(--line)" }}>
-            <NavPill href="/" active={pathname === "/"} icon={<Home size={14} />}>
+          <nav className="hidden lg:flex items-center gap-1.5 pl-3" style={{ borderLeft: "1px solid var(--line)" }}>
+            <NavPill href="/" active={pathname === "/"} icon={<Home size={15} />}>
               首页
             </NavPill>
+            <NavPill
+              href="/boards"
+              active={pathname === "/boards" || pathname?.startsWith("/board/") === true}
+              icon={<LayoutGrid size={15} />}
+            >
+              板块
+            </NavPill>
           </nav>
         </div>
 
-        {/* 中部留白：为后续主导航菜单项预留位置 */}
+        {/* 中部弹性留白，把搜索与操作区推到右侧 */}
         <div className="hidden lg:block flex-1" aria-hidden />
 
         {/* 右侧操作区：搜索靠右停靠 + 桌面/移动共用铃铛（仅挂载一次，避免重复轮询），
@@ -370,6 +378,12 @@ export default function Header({
           </form>
           <div className="flex flex-col">
             <MobileLink href="/" active={pathname === "/"}>首页</MobileLink>
+            <MobileLink
+              href="/boards"
+              active={pathname === "/boards" || pathname?.startsWith("/board/") === true}
+            >
+              板块
+            </MobileLink>
             {user && <MobileLink href="/compose">发帖</MobileLink>}
             {user && (
               <MobileLink href="/chat" active={pathname?.startsWith("/chat") ?? false}>
@@ -431,11 +445,11 @@ function NavPill({
   return (
     <Link
       href={href}
-      className="inline-flex items-center gap-1.5 px-3.5 py-2 rounded-full text-[13.5px] transition-colors"
+      className="inline-flex items-center gap-1.5 px-3.5 py-2 rounded-full text-[15px] font-semibold transition-colors"
       style={
         active
           ? { background: "var(--accent-soft)", color: "var(--accent)" }
-          : { color: "var(--ink-2)" }
+          : { color: "var(--ink)" }
       }
     >
       {icon}
@@ -456,7 +470,7 @@ function MobileLink({
   return (
     <Link
       href={href}
-      className="px-3 py-3 rounded-2xl text-[15px] transition-colors"
+      className="px-3 py-3 rounded-2xl text-[16px] font-semibold transition-colors"
       style={{
         color: active ? "var(--accent)" : "var(--ink)",
         background: active ? "var(--accent-soft)" : "transparent",