Add skill-creator plugin

plugins/skill-creator/.claude-plugin/plugin.json

@@ -0,0 +1,8 @@
+{
+  "name": "skill-creator",
+  "description": "Create new skills, improve existing skills, and measure skill performance. Use when users want to create a skill from scratch, update or optimize an existing skill, run evals to test a skill, or benchmark skill performance with variance analysis.",
+  "author": {
+    "name": "Anthropic",
+    "email": "support@anthropic.com"
+  }
+}