chore: update @modelcontextprotocol/sdk peer dependency restriction to allow minor version updates

• The modelcontextprotocol/sdk dependency has already released version 1.29.0 (npm package).
• If an application depends on both modelcontextprotocol/sdk and mcp-handler, it cannot upgrade modelcontextprotocol/sdk due to the peerDependencies defined in mcp-handler.

This PR resolves that issue while still enforcing a minimum version of 1.26.0 for modelcontextprotocol/sdk, as defined in https://github.com/vercel/mcp-handler/pull/150