use MinIO to save the chart image base64 and return the url. #10
Description
- MinIO：https://min.io/
- Add an MCP environment variable to record the MinIO key.
Using a URL has the following advantages over Base64:
- Reduces the number of tokens output by the LLM.
- Provides long-term accessibility and enables sharing and transfer.
- Offers a better experience for most MCP clients.