Add superpowers plugin to marketplace (#148)

- Added superpowers plugin entry to marketplace.json
- Plugin provides brainstorming, subagent driven development, code review, debugging, and TDD capabilities
- Plugin also teaches Claude how to author and test new skills

Co-authored-by: Claude <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -566,6 +566,16 @@
         "url": "https://github.com/circlebackai/claude-code-plugin.git"
       },
       "homepage": "https://github.com/circlebackai/claude-code-plugin.git"
+    },
+    {
+      "name": "superpowers",
+      "description": "Superpowers teaches Claude brainstorming, subagent driven development with built in code review, systematic debugging, and red/green TDD. Additionally, it teaches Claude how to author and test new skills.",
+      "category": "development",
+      "source": {
+        "source": "url",
+        "url": "https://github.com/obra/superpowers.git"
+      },
+      "homepage": "https://github.com/obra/superpowers.git"
     }
   ]
 }