feat(storage): add ObjectStorage interface and MinIO client

Add ObjectStorage interface (11 methods) with MinioClient implementation using minio-go Core.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/storage/minio_test.go

@@ -0,0 +1,7 @@
+package storage
+
+import "testing"
+
+func TestMinioClientImplementsObjectStorage(t *testing.T) {
+	var _ ObjectStorage = (*MinioClient)(nil)
+}