[ENGINEERING] Preferred days

[yxli001]

What is the issue?
Implement the preferred days feature on the calendar.

• Design
• On hover over a column header, show a star outline to the left of the column header, feel free to use icons from lucide-react.
• When the star icon is clicked, set schedulePreferences.preferredDays (chekout page.tsx for examples of using the state store hooks) accordingly. If you feel comfortable, it may be easier to change this field to a boolean array of length five to indicate each day being preferred or not. But this requires updating the scheduling algorithm as well, so it's up to you if you want to explore that.
• The Full Calendar API is kind of a pain in the ass to work with, Copilot is pretty good at it or you can also ask @b-jonathan if you have any questions.