feat: QR-Custom Payment + mode webhook secret GOWA

- tabel custom_qr_payments, service, halaman admin + publik share
- kode unik 20 menit, warning bila bayar setelah batas, manual pay/accept/reject
- webhook payment-notif mencocokkan nominal custom
- menu sidebar QR-Custom Payment
- GOWA secret: auto generate (locked) / manual (simpan lalu locked, ubah)
- versi 0.6.0

package.json

@@ -1,6 +1,6 @@
 {
   "name": "open-isp",
-  "version": "0.5.20",
+  "version": "0.6.0",
   "description": "OPEN-ISP \u2014 sistem billing & manajemen ISP open-source (PWA pelanggan, multi-OLT, RADIUS, WhatsApp, QRIS)",
   "main": "app-customer.js",
   "scripts": {