Drop Node suffix from the playground's default example program

The last example still using the old convention: CustomerNode -> Customer.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: YoanSallami

docs/javascripts/playground.js

@@ -27,8 +27,8 @@
     "  orders(order_id:, customer_id:, amount:, created_at:);",
     "",
     "# Concepts",
-    "@OrderBy(CustomerNode, \"customer_id\");",
-    "CustomerNode(customer_id:) distinct :- Orders(customer_id:);",
+    "@OrderBy(Customer, \"customer_id\");",
+    "Customer(customer_id:) distinct :- Orders(customer_id:);",
     "",
     "# Rules",
     "@OrderBy(CustomerRevenue, \"total\", \"desc\");",