Download a file using the specified file path and file name

Retrieves a file from the file store and returns it as a downloadable response.
It handles the following:

• URL decoding of the file path to support special characters
• Determining the appropriate content type based on file extension
• Setting response headers including content length and modified date
• Adding file path information for client reference

If the requested file is not found, it returns a 404 Not Found response.