fix: Description Length Limit

[Kelketek]

This PR adds a check for descriptions which exceed the 2000 character limit imposed by Artconomy, providing an error when present.

Testing instructions:

1. Log into an Artconomy account
2. Create a file submission
3. Enter a default description with a length over 2000 characters
4. Verify error message shown upon save
5. Replace default description with one that is shorter than 2000 characters
6. Add a description override for Artconomy with a length greater than 2000 characters
7. Verify error message shown upon save

[askmeaboutlo0m]

The description validation check is incorrect, it just grabs the description in HTML format and uses its length. Compare with how other website services do it.

[Kelketek]

Thanks, @askmeaboutlo0m ! That solution is also far more concise. I've updated the code.