Add command to encrypt all files if no argument is provided

[heavenly999]

Story/Issue Link

Issue #60

Background

• For the add command, we will ensure it encrypts all files when no argument is provided and will add checks to determine the existence of both encrypted and non-encrypted files on disk.
• The decrypt command will receive safety checks to confirm the presence of encrypted files on the disk, coupled with additional log messages to keep users informed.
• Lastly, in the exec command, we'll implement a deferred file handler close to optimize resource management.

[onyxraven]

Hey, just wanted to reply back that I've seen the PR and will review it closer later in the week :)