Remove SHA pin from miro entry

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

@@ -886,6 +886,21 @@
       },
       "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.",