fix(conductor): remove invalid category field from plugin.json

The category field is not part of the valid plugin manifest schema,
causing installation to fail with "Unrecognized key: category" error.

conductor/.claude-plugin/plugin.json

@@ -16,6 +16,5 @@
     "planning",
     "specifications",
     "workflow"
-  ],
-  "category": "workflows"
+  ]
 }