UI and Accessibility improvements for tag table

[jesperhodge]

AC:

• Add highlight around newly added rows while they are not yet sorted in place
• Add hints to disabled button to communicate why they are disabled (tooltips?) for accessibility
• Style input row according to Figma / UX decisions (to be determined)
• When a forbidden character is used, the error message should specify which characters are forbidden.

(Update 2026-03-31)

• Increase input box size (maybe dynamically)
  see https://github.com/openedx/frontend-app-authoring/pull/2939/changes#r3016228803