fix: prevent trailing slash redirects for API routes

Adds skipTrailingSlashRedirect to prevent HTTP 301 redirects
  on API endpoints like /api/stripe/webhook. This ensures
  webhooks and external integrations work reliably.

  🤖 Generated with Claude Code

next.config.mjs

@@ -1,6 +1,7 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
   output: 'standalone',
+  skipTrailingSlashRedirect: true,
   images: {
     unoptimized: false,
     domains: ['www.qrmaster.net', 'qrmaster.net', 'images.qrmaster.net'],