move description to marketplace

Author: twishabansal

.claude-plugin/marketplace.json

@@ -4,11 +4,13 @@
     "name": "Google LLC",
     "email": "data-cloud-ai-integrations@google.com"
   },
+  "metadata": {
+    "description": "Agent skills for Cloud SQL for PostgreSQL to query, manage, and monitor databases."
+  },
   "plugins": [
     {
       "name": "cloud-sql-postgresql",
-      "source": "./",
-      "description": "Agent skills for Cloud SQL for PostgreSQL to query, manage, and monitor databases."
+      "source": "./"
     }
   ]
 }