Add Web Push warning notification backend

app/api/notifications/vapid-key/route.ts

@@ -0,0 +1,11 @@
+import { NextResponse } from "next/server";
+import { getVapidPublicKey, isWebPushConfigured } from "@/lib/push-service";
+
+export const runtime = "nodejs";
+
+export function GET() {
+  return NextResponse.json({
+    configured: isWebPushConfigured(),
+    publicKey: getVapidPublicKey(),
+  });
+}