add(plugin): mcp-server-dev — skills for building MCP servers

Three skills guiding developers through MCP server design:
- build-mcp-server: entry-point decision guide (remote HTTP vs MCPB vs local)
- build-mcp-app: interactive UI widgets rendered in chat
- build-mcpb: bundled local servers with runtime

Includes reference files for scaffolds, tool design, auth (DCR/CIMD),
widget templates, manifest schema, and local security hardening.

.claude-plugin/marketplace.json

@@ -946,6 +946,17 @@
         "sha": "b93007e9a726c6ee93c57a949e732744ef5acbfd"
       },
       "homepage": "https://github.com/zapier/zapier-mcp/tree/main/plugins/zapier"
+    },
+    {
+      "name": "mcp-server-dev",
+      "description": "Skills for designing and building MCP servers that work seamlessly with Claude. Guides you through deployment models (remote HTTP, MCPB, local), tool design patterns, auth, and interactive MCP apps.",
+      "author": {
+        "name": "Anthropic",
+        "email": "support@anthropic.com"
+      },
+      "source": "./plugins/mcp-server-dev",
+      "category": "development",
+      "homepage": "https://github.com/anthropics/claude-plugins-official/tree/main/plugins/mcp-server-dev"
     }
   ]
 }