Create link error message and bug fix

[marcusljf]

Changed the error message from "Invalid key" to "Enter a valid short link".

Found a bug that the destination URL allowed spaces, and then those links went to 404 pages. So now it shows an error if the user tries to create a short link with spaces in the destination url.

Summary by CodeRabbit

• Bug Fixes

  • Improved URL input validation to prevent whitespace characters in relevant forms.
  • Enhanced error messaging for invalid short link entries, providing clearer guidance to users.

• Style

  • Minor code cleanup for better readability (no impact on functionality).