fix: migrate S3 bucket interactions to Python MinIO SDK

Summary

Migrate from aioboto3/botocore to the official MinIO Python SDK (minio>=7.2.5) for S3-compatible object storage operations. This change ensures compatibility with corpus-server-app and resolves issues encountered with Boto.

Changes

Dependency Migration

• Replace aioboto3>=13.1.1 and botocore>=13.1.1 with minio>=7.2.5 in pyproject.toml
• Update uv.lock with new dependency tree

Code Updates (upload.py)

• Replace aioboto3.Session and botocore.config.Config with minio.Minio client
• Update endpoint URL parsing to extract host and secure flag for MinIO client initialization
• Convert async Boto calls to threaded blocking calls using asyncio.to_thread():
  • client.fget_object() for file downloads
  • client.list_objects() for object listing
• Remove Boto-specific paginator logic in favor of MinIO's list_objects() API
• Remove unused urllib.parse.urlencode import (now using urlparse)

Test Updates (test_s3_upload.py)

• Update tests to reflect MinIO SDK usage

Why This Change?

1. Compatibility: Aligns with corpus-server-app which uses the MinIO SDK
2. Boto Issues: Resolves compatibility issues with Boto's async behavior and configuration complexity
3. Simpler API: MinIO SDK provides a cleaner, more direct API for S3-compatible operations
4. Reduced Dependencies: Removes aioboto3 and botocore in favor of a single lightweight SDK