Execute an MCP tool.

Accepts tool name and arguments, executes the tool, and returns the result in MCP TextContent format.

Example request:

{
  "name": "lookup_icd10_code",
  "arguments": {"code": "E11.22"}
}

Example response:

{
  "content": [
    {
      "type": "text",
      "text": "{\"code\": \"E11.22\", \"description\": \"Type 2 diabetes...\", ...}"
    }
  ]
}