refactor: migrate from deprecated s3/manager to s3/transfermanager

Replace feature/s3/manager (deprecated) with feature/s3/transfermanager.
Updates Uploader interface, constructor, and all tests to use the new
UploadObject API with transfermanager types.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

s3.go

@@ -8,13 +8,13 @@ import (
 	"github.com/aws/aws-sdk-go-v2/aws"
 	v4 "github.com/aws/aws-sdk-go-v2/aws/signer/v4"
 	"github.com/aws/aws-sdk-go-v2/config"
-	"github.com/aws/aws-sdk-go-v2/feature/s3/manager"
+	"github.com/aws/aws-sdk-go-v2/feature/s3/transfermanager"
 	"github.com/aws/aws-sdk-go-v2/service/s3"
 )
 
-// Uploader is the interface for uploading objects to S3 using the upload manager
+// Uploader is the interface for uploading objects to S3 using the transfer manager
 type Uploader interface {
-	Upload(ctx context.Context, input *s3.PutObjectInput, opts ...func(*manager.Uploader)) (*manager.UploadOutput, error)
+	UploadObject(ctx context.Context, input *transfermanager.UploadObjectInput, opts ...func(*transfermanager.Options)) (*transfermanager.UploadObjectOutput, error)
 }
 
 // DirectUploader is the interface for uploading objects directly to S3
@@ -45,7 +45,7 @@ func (s *S3) Store(path string, content io.Reader, contentType string) (string,
 }
 
 func (s *S3) storeWithManager(path string, content io.Reader, contentType string) (string, error) {
-	out, err := s.svc.Upload(context.Background(), &s3.PutObjectInput{
+	out, err := s.svc.UploadObject(context.Background(), &transfermanager.UploadObjectInput{
 		Bucket: aws.String(s.bucket),
 		Key:    aws.String(path),
 		Body:   content,
@@ -100,8 +100,8 @@ func New(bucket string) (*S3, error) {
 		return nil, err
 	}
 	client := s3.NewFromConfig(cfg)
-	uploader := manager.NewUploader(client, func(u *manager.Uploader) {
-		u.PartSize = 5 * 1024 * 1024
+	uploader := transfermanager.New(client, func(o *transfermanager.Options) {
+		o.PartSizeBytes = 5 * 1024 * 1024
 	})
 	presignClient := s3.NewPresignClient(client)
 	return &S3{