Optimize MinIO upload streaming

[hequan2017]

Motivation

• Reduce memory usage and improve reliability for large uploads by streaming directly from the multipart file and ensuring file handles are closed.

Description

• Update UploadFile to stream from the multipart.File by passing f to PutObject instead of buffering into a bytes.Buffer.
• Add defer f.Close() to ensure the uploaded file handle is closed and remove the now-unused in-memory copy and imports.
• Preserve existing timeout and MIME detection logic and keep bucket creation/initialization behavior unchanged.

Testing

• No automated tests were run for this change.

---

Codex Task