Make SITE_URL and AUTH_SECRET configurable via environment variables for any deployment

.env.example

@@ -0,0 +1,9 @@
+# Site Configuration
+# The public URL where your application will be hosted
+# This is used for QR codes and other absolute URLs
+SITE_URL=https://your-domain.com
+
+# Authentication Secret
+# Generate a secure random string for production
+# You can use: openssl rand -hex 32
+AUTH_SECRET=change-this-secret-in-production