fix(admin): persist data directory and pass env vars

app/api/admin/login/route.ts

@@ -0,0 +1,16 @@
+import { NextResponse } from "next/server";
+import { adminCookieOptions, adminSessionCookie, createAdminSession, validateAdminCredentials } from "@/lib/admin/auth";
+
+export async function POST(request: Request) {
+  const form = await request.formData();
+  const email = String(form.get("email") ?? "");
+  const password = String(form.get("password") ?? "");
+
+  if (!validateAdminCredentials(email, password)) {
+    return NextResponse.json({ message: "Ungültige Zugangsdaten." }, { status: 401 });
+  }
+
+  const response = NextResponse.json({ message: "Anmeldung erfolgreich." });
+  response.cookies.set(adminSessionCookie, createAdminSession(), adminCookieOptions());
+  return response;
+}