[web] [fix] [ENG-965] calendar hover history + add show on hover

Summary:
on hover, add and history prompt are now visible
https://linear.app/comm/issue/ENG-965/calendar-buttons-only-visible-on-hover

Test Plan: hover over days on the calendar

Reviewers: atul, palys-swm, def-au1t

Reviewed By: palys-swm

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3639