fix: move marketplace to .claude-plugin folder

.claude-plugin/marketplace.json

@@ -0,0 +1,18 @@
+{
+  "name": "puelpan-claude",
+  "owner": {
+    "name": "Juan Puelpan",
+    "email": "juan@puelpan.com"
+  },
+  "plugins": [
+    {
+      "name": "github",
+      "source": "./github",
+      "description": "Git and Github utility commands",
+      "version": "1.0.0",
+      "author": {
+        "name": "Juan Puelpan"
+      }
+    }
+  ]
+}