feat: 添加单个代码片段展示页面的数据库查询和404处理

src/app/snippets/[id]/page.tsx

@@ -1,3 +1,6 @@
+import { db } from "@/db";
+import { notFound } from "next/navigation";
+
 interface SnippetShowPageProps {
   params: Promise<{
     id: string;
@@ -5,6 +8,16 @@ interface SnippetShowPageProps {
 }
 
 export default async function SnippetShowPage(props: SnippetShowPageProps) {
-  const { id } = await props.params;
-  return <div>Show a snippet: {id}</div>;
+  const params = await props.params;
+  const snippet = await db.snippet.findFirst({
+    where: {
+      id: parseInt(params.id),
+    },
+  });
+
+  if (!snippet) {
+    return notFound();
+  }
+
+  return <div>Show a snippet: {snippet.title}</div>;
 }