Use file model MIME type instead of S3 content type

GetFileBase64 read the MIME type from the S3 response header,
which can be application/octet-stream for files uploaded without
an explicit content type. Use file.GetMimeType() from the
database instead, which stores the correct MIME type captured
at upload time. This fixes evidence description failures when
calling the OpenAI API with PDF files.

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/filemanager/service.go

@@ -65,12 +65,8 @@ func (s *Service) GetFileBase64(
 		return "", "", fmt.Errorf("cannot read file data: %w", err)
 	}
 
-	if result.ContentType == nil || *result.ContentType == "" {
-		return "", "", fmt.Errorf("no MIME type available for file %s", file.GetObjectKey())
-	}
-
 	base64Data = base64.StdEncoding.EncodeToString(fileData)
-	mimeType = *result.ContentType
+	mimeType = file.GetMimeType()
 
 	return base64Data, mimeType, nil
 }