feat(mastra): add MCP docs server configuration (#143)

Add mcpServers entry to plugin.json to integrate @mastra/mcp-docs-server
via npx, enabling MCP-based documentation access for the Mastra plugin.

Author: amondnet

plugins/mastra/.claude-plugin/plugin.json

@@ -14,5 +14,12 @@
     "framework",
     "agent"
   ],
+  "mcpServers": {
+    "mastra": {
+      "type": "stdio",
+      "command": "npx",
+      "args": ["-y", "@mastra/mcp-docs-server@latest"]
+    }
+  },
   "skills": "./.agents/skills/"
 }