Improve UX for file sharing modal

[Igor Shadurin]

The current file sharing modal could be more user-friendly. Right now, the sharing code appears a bit later after the modal shows, which might confuse the user. Here's what needs to be done to improve this:

1. Show a spinner while waiting for the sharing code to be generated.
2. Hide the "Copy" button during this time.
3. Once the sharing code is available, hide the spinner and show the "Copy" button.

Also, the button labeled "Complete Sharing" only closes the modal and doesn't actually complete any sharing process. I suggest renaming it to just "OK" for clarity.

sharing-file.mov