Replace VitePress docs with Next.js redirect app for domain migration

[Copilot]

docs.gopeed.com is being consolidated under gopeed.com — all traffic needs permanent 301 redirects to gopeed.com/docs, with multilingual paths (e.g. /zh/install.html) mapped to gopeed.com/zh/docs/install.

Changes

• Removed: entire VitePress site (.vitepress/, docs/, build.sh, pnpm-lock.yaml, vercel.json)
• Added: minimal Next.js 15 app whose sole purpose is redirecting via middleware.ts:
  • Strips .html extension
  • Detects /zh and /zh-TW language prefixes and preserves them before /docs/
  • Falls back to gopeed.com/docs{path} for all other routes
• Updated: CI workflow — removed pnpm/action-setup step (project now uses npm)

Redirect logic

// /zh/install.html  → https://gopeed.com/zh/docs/install
// /install.html     → https://gopeed.com/docs/install
// /zh/some/path     → https://gopeed.com/zh/docs/some/path
// /                 → https://gopeed.com/docs/

const cleanPath = pathname.endsWith(".html") ? pathname.slice(0, -5) : pathname;
const langMatch = cleanPath.match(/^\/(zh|zh-TW)(\/.*)?$/);

destination = langMatch
  ? `https://gopeed.com/${langMatch[1]}/docs${langMatch[2] ?? ""}`
  : `https://gopeed.com/docs${cleanPath}`;

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[monkeyWie]

@copilot 确保本地测试能重定向正确，另外要确保CI部署到vercel上没问题

[Copilot]

@copilot 确保本地测试能重定向正确，另外要确保CI部署到vercel上没问题

本地测试全部通过，所有场景均返回 301 且 Location 正确：

✓ /zh/install.html     →  https://gopeed.com/zh/docs/install
✓ /zh-TW/install.html  →  https://gopeed.com/zh-TW/docs/install
✓ /install.html        →  https://gopeed.com/docs/install
✓ /zh/some/path        →  https://gopeed.com/zh/docs/some/path
✓ /some/path           →  https://gopeed.com/docs/some/path
✓ /                    →  https://gopeed.com/docs/
✓ /dev-api.html        →  https://gopeed.com/docs/dev-api
✓ /zh-TW/dev.html      →  https://gopeed.com/zh-TW/docs/dev

浏览器访问 localhost:3099/zh/install.html 后自动跳转到 gopeed.com/zh/docs/install：

关于 CI 部署到 Vercel：

• Vercel 会自动识别 Next.js 框架，无需额外配置
• CI 已移除 pnpm setup 步骤，改用 npm（项目已切换为 npm）
• vercel build --prod 和 vercel deploy --prebuilt --prod 流程不变，兼容 Next.js 项目