Add default /docs route to list information about the HTTP MCP server

Is your feature request related to a problem? Please describe.
Would be useful to have an equivalent to something like how FastAPI generates OpenAPI docs and are automatically accessible at /docs route.

Describe the solution you'd like
Add a /docs route to the starlette app that provides information about the mcp server (available tools, prompts, resources, version, etc.)

Describe alternatives you've considered
none

Additional context
Basic example I currently use:

該 issue 沒有指定檔案或測試；先找出 Starlette 應用程式及其現有的 HTTP 路由設定。根據 MCP 伺服器的工具、提示、資源和版本定義 /docs 回應，然後確認該路由是否公開預期的資訊。