feat(app): add app.liambx.com to server action allowed origins

As part of the subdomain migration (Issue #5234), add app.liambx.com
to the allowed origins for Next.js server actions to prepare for
the transition from liambx.com/app/* to app.liambx.com.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: hoshinotsuyoshi

frontend/apps/app/next.config.ts

@@ -23,7 +23,7 @@ const nextConfig: NextConfig = {
     serverActions: {
       allowedOrigins:
         process.env.VERCEL_ENV === 'production'
-          ? ['liambx.com', 'liam-erd-web.vercel.app']
+          ? ['liambx.com', 'liam-erd-web.vercel.app', 'app.liambx.com']
           : undefined,
     },
   },
@@ -37,6 +37,10 @@ const nextConfig: NextConfig = {
         protocol: 'https',
         hostname: 'liam-erd-web.vercel.app',
       },
+      {
+        protocol: 'https',
+        hostname: 'app.liambx.com',
+      },
     ],
   },
   serverExternalPackages: ['@electric-sql/pglite'],