fix(a11y): ink-400 对比度达标,接入 Noto Serif SC webfont,补纸张噪点与入场编排

- ink-400 #9C9587(2.90:1)→ #756F61(paper-50 4.87:1 / paper-100 4.55:1),正文级小字全部达标
- serif 栈插入 Noto Serif SC(fontsource 子集加载),Windows 不再跌进 SimSun
- 首页加 feTurbulence 纸张噪点层(.grain);报头/赛程行/预测版 rise-in 错峰入场(60ms 步进)
- reduce 动效用户:隐藏态与动画同在 no-preference 块,不会白屏
- Switch 提到模块顶层(修 render 重建丢焦点);a→Link(SPA 内链);h3→h2/h4→h3 修标题层级
- 按钮/输入热区抬高(btn 40px / btn-sm 32px / field py-2);index.css 硬编码色值改 :root 令牌

frontend/src/App.tsx

@@ -6,7 +6,7 @@
  * - /admin/* → 管理后台
  */
 
-import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom'
+import { BrowserRouter, Routes, Route, Navigate, Link } from 'react-router-dom'
 import { ErrorBoundary } from './components/ErrorBoundary'
 import Matches from './pages/Matches'
 import { adminRoutes } from './admin/routes'
@@ -23,9 +23,10 @@ function dateLine(): string {
 
 function HomePage() {
   return (
-    <div className="min-h-screen bg-paper-50">
+    // grain: 纸张噪点氛围层;报头、赛程行、预测版各自带 rise-in 入场
+    <div className="grain min-h-screen bg-paper-50">
       {/* ── 报头:粗线 + 居中刊名 + 报眉 ── */}
-      <header className="masthead-rule">
+      <header className="masthead-rule rise-in">
         <div className="mx-auto max-w-5xl px-5 sm:px-8">
           <div className="border-b border-ink-900 py-5 text-center sm:py-6">
             <h1 className="font-serif text-4xl font-bold tracking-widest text-ink-900">
@@ -40,13 +41,13 @@ function HomePage() {
           </div>
           <div className="flex items-center justify-between border-b border-ink-200 py-2 text-2xs text-ink-500">
             <span>{dateLine()}</span>
-            <a
-              href="/admin"
-              className="flex items-center gap-1.5 text-press hover:text-press-dark transition-colors"
+            <Link
+              to="/admin"
+              className="flex min-h-[32px] items-center gap-1.5 text-press transition-colors hover:text-press-dark"
             >
               <span aria-hidden="true">⚙</span>
               管理后台
-            </a>
+            </Link>
           </div>
         </div>
       </header>