完善文档与前端迁移，补充开源协议

web/src/app/not-found.tsx

@@ -0,0 +1,24 @@
+import Link from "next/link";
+
+import { Button } from "@/components/ui/button";
+import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
+
+export default function NotFound() {
+  return (
+    <main className="flex min-h-screen items-center justify-center p-6">
+      <Card className="max-w-lg border-slate-200/70 bg-white/90">
+        <CardHeader>
+          <CardTitle>页面不存在</CardTitle>
+        </CardHeader>
+        <CardContent className="space-y-4">
+          <p className="text-sm leading-6 text-slate-600">
+            这个路由还没有迁入新的 Next.js 前端，或者你访问了一个不存在的地址。
+          </p>
+          <Button asChild>
+            <Link href="/dashboard">返回仪表盘</Link>
+          </Button>
+        </CardContent>
+      </Card>
+    </main>
+  );
+}