Publish threejs skill to marketplace

Constraint: Public skills are published only by explicit administrator action unless they are tracked third-party market sources.
Confidence: high
Scope-risk: narrow
Directive: Keep private/internal skills out of the public marketplace.
Tested: Marketplace validation passed.

.agents/plugins/marketplace.json

@@ -75,6 +75,18 @@
         "authentication": "ON_INSTALL"
       },
       "category": "文档处理"
+    },
+    {
+      "name": "threejs",
+      "source": {
+        "source": "local",
+        "path": "./plugins/codex/plugins/threejs"
+      },
+      "policy": {
+        "installation": "AVAILABLE",
+        "authentication": "ON_INSTALL"
+      },
+      "category": "设计"
     }
   ]
 }