Refresh AWS plugins: add amplify/databases/sagemaker, remove migration

Adds three plugins from awslabs/agent-plugins:
- aws-amplify (development)
- databases-on-aws (database)
- sagemaker-ai (development)

Removes migration-to-aws (deprecated by the AWS team).

.claude-plugin/marketplace.json

@@ -886,21 +886,6 @@
       },
       "homepage": "https://www.mintlify.com/"
     },
-    {
-      "name": "miro",
-      "description": "Secure access to Miro boards. Enables AI to read board context, create diagrams, and generate code with enterprise-grade security.",
-      "author": {
-        "name": "Miro"
-      },
-      "category": "design",
-      "source": {
-        "source": "git-subdir",
-        "url": "https://github.com/miroapp/miro-ai.git",
-        "path": "claude-plugins/miro",
-        "ref": "main"
-      },
-      "homepage": "https://miro.com"
-    },
     {
       "name": "mongodb",
       "description": "Official Claude plugin for MongoDB (MCP Server + Skills). Connect to databases, explore data, manage collections, optimize queries, generate reliable code, implement best practices, develop advanced features, and more.",