docs(tools): add ToolSDK MCP Registry to tools list

[Seey215]

Background

The MCP Tools section aims to provide developers with a clear overview of publicly available MCP servers.
Before this change, the list did not include the ToolSDK MCP Registry, which is a privately deployable registry with seamless one-line integration via toolsdk.ai.
Adding it improves discoverability for developers who want to manage their MCP tools in self-hosted or enterprise environments.

Summary

Added the ToolSDK MCP Registry entry to the MCP Tools list in the documentation:

- **[ToolSDK MCP Registry](https://github.com/toolsdk-ai/toolsdk-mcp-registry)** - A privately deployable MCP Registry with one-line AI SDK integration via **toolsdk.ai**. (See: [AI SDK Integration](https://toolsdk.ai/docs/tutorials/getting-started#ai-sdk))

No functional changes; documentation update only.

Manual Verification

Not applicable — documentation-only change.

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Future Work

Potentially add more usage examples or guidance on integrating third-party MCP registries with the AI SDK.

Related Issues

None.