feat: add announcements feature with dynamic routing and markdown support

app/announcements/page.tsx

@@ -0,0 +1,49 @@
+import Link from "next/link";
+
+import { Badge } from "@/components/ui/badge";
+import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card";
+import { getAllAnnouncements } from "@/lib/announcements";
+
+export const metadata = {
+  title: "お知らせ | Takasumi-Neodyマイクラサーバプロジェクト",
+  description: "Takasumi-Neodyマイクラサーバプロジェクトのお知らせ一覧です。",
+};
+
+export default async function AnnouncementsPage() {
+  const announcements = await getAllAnnouncements();
+
+  return (
+    <div className="mx-auto flex w-full max-w-5xl flex-1 flex-col gap-6 px-4 py-8 sm:px-8 sm:py-12">
+      <header className="rounded-3xl border bg-card/70 p-6 shadow-sm backdrop-blur sm:p-8">
+        <Badge variant="outline" className="mb-3">
+          お知らせ
+        </Badge>
+        <h1 className="text-3xl font-semibold tracking-tight sm:text-4xl">更新情報・告知</h1>
+        <p className="mt-3 text-sm leading-7 text-muted-foreground sm:text-base">
+          このページは Markdown で作成したお知らせを表示します。
+        </p>
+      </header>
+
+      <section className="grid gap-4">
+        {announcements.map((item) => (
+          <Card key={item.slug} className="border-foreground/10">
+            <CardHeader>
+              <p className="text-xs text-muted-foreground">{item.date}</p>
+              <CardTitle className="text-xl">
+                <Link
+                  href={`/announcements/${item.slug}`}
+                  className="underline-offset-4 hover:underline"
+                >
+                  {item.title}
+                </Link>
+              </CardTitle>
+            </CardHeader>
+            <CardContent>
+              <p className="text-sm text-muted-foreground">{item.summary}</p>
+            </CardContent>
+          </Card>
+        ))}
+      </section>
+    </div>
+  );
+}