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/package.json

@@ -9,6 +9,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@fontsource/noto-serif-sc": "^5.3.0",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
     "react-router-dom": "^6.30.6"