feat: Add explanatory-output-style and learning-output-style plugins to marketplace

Added two missing plugins to the marketplace.json:
- explanatory-output-style: Adds educational insights about implementation choices
- learning-output-style: Interactive learning mode that requests code contributions

Both plugins are categorized under "learning" to help users discover educational tools.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -68,6 +68,28 @@
       },
       "source": "./plugins/code-review",
       "category": "productivity"
+    },
+    {
+      "name": "explanatory-output-style",
+      "description": "Adds educational insights about implementation choices and codebase patterns (mimics the deprecated Explanatory output style)",
+      "version": "1.0.0",
+      "author": {
+        "name": "Dickson Tsai",
+        "email": "dickson@anthropic.com"
+      },
+      "source": "./plugins/explanatory-output-style",
+      "category": "learning"
+    },
+    {
+      "name": "learning-output-style",
+      "description": "Interactive learning mode that requests meaningful code contributions at decision points (mimics the unshipped Learning output style)",
+      "version": "1.0.0",
+      "author": {
+        "name": "Boris Cherny",
+        "email": "boris@anthropic.com"
+      },
+      "source": "./plugins/learning-output-style",
+      "category": "learning"
     }
   ]
 }