fix(web): add libsodium-wrappers to serverExternalPackages

Missing from standalone output → invite creation crashes with
'Cannot find module libsodium-wrappers' in production.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/next.config.ts

@@ -92,6 +92,7 @@ const config: NextConfig = {
     "@payloadcms/ui",
     "react-image-crop",
     "sharp",
+    "libsodium-wrappers",
   ],
   turbopack: {
     rules: {