Feature for adding notes to text of vision book

[phi-jkim]

Added a feature for students to be able to write notes on the text sections that is stored in local storage.

Changes:

• add sticky-note overlay that lets readers place draggable notes anywhere on a page
• persist notes per page using localStorage with document-relative coordinates so scrolling keeps them aligned
• inform users via hint, tooltip, and ARIA label that notes are stored locally

[shensquared]

Hi Jinha! Thanks for this PR too!
(Sorry that the team has all been a bit occupied with the Fall semester going. Will take a closer look during the break.)