Reapply "Add missing admin action files and navigation links"

This reverts commit 4d515bc400.

src/actions/soundtracks.ts

@@ -0,0 +1,20 @@
+"use server";
+
+import { revalidatePath } from "next/cache";
+import { requireStaff } from "@/lib/admin/guard";
+import { prisma } from "@/lib/prisma";
+
+export async function deleteSoundtrack({ id }: { id: number }) {
+  await requireStaff();
+  await prisma.soundtracks.delete({ where: { id } });
+  revalidatePath("/admin/sounds");
+}
+
+export async function updateSoundtrack({ id, name, author, track, length }: { id: number; name: string; author: string; track: string; length: number }) {
+  await requireStaff();
+  await prisma.soundtracks.update({
+    where: { id },
+    data: { name, author, track, length },
+  });
+  revalidatePath("/admin/sounds");
+}