Prevent process the same file

When uploading the file we need to save the original file name and check which file already been stored. After uploading the file we'll need to show results of the files which rejected.

Start by locating the file-upload handling and the code that records stored files. Trace how upload results reach the interface, then define completion as preserving each original filename, rejecting already stored files, and showing which files were rejected after upload.

Written by the indexing model from the issue text.