fix: improve env onboarding and dev error messages

apps/student/next.config.mjs

@@ -2,6 +2,7 @@
 import path from 'path';
 
 const __dirname = path.resolve();
+const adminDomain = process.env.ADMIN_DOMAIN || "http://localhost:9001";
 
 const nextConfig = {
   transpilePackages: ['@workspace/ui', '@workspace/db'],
@@ -11,15 +12,15 @@ const nextConfig = {
     return [
         {
             source: '/admin',
-            destination: `${process.env.ADMIN_DOMAIN}/admin`,
+            destination: `${adminDomain}/admin`,
         },
         {
             source: '/admin/:path+',
-            destination: `${process.env.ADMIN_DOMAIN}/admin/:path+`,
+            destination: `${adminDomain}/admin/:path+`,
         },
         {
             source: '/admin-static/:path+',
-            destination: `${process.env.ADMIN_DOMAIN}/admin-static/:path+`,
+            destination: `${adminDomain}/admin-static/:path+`,
         }
     ];
 }