Add character limit support for description editor (ReactQuill)

Description

The ReactQuill editor used for the course/description input currently allows unlimited characters. This can lead to excessively long text entries, causing usability and validation issues.

We need to enforce a maximum character limit of 1000 characters (plain text only), while ensuring that existing responsiveness, styling, and functionality remain unaffected.

Expected Behavior

Users should not be able to type more than 1000 characters.

A live character counter should display the current count (e.g., 250/1000).

If the field is left empty, a validation error should still be shown.