Store Calendar Data

[sun-415]

Updated user story: As a user, I want my calendar data to be saved, so that I can access my progress seamlessly across devices and sessions.

Acceptance Criteria:

• Each time the user completes the questionnaire, the date and completion status are saved to the backend, linked to the user’s unique account ID.
• When the user accesses the Progress page, the app retrieves calendar data from the backend to display an up-to-date calendar.
• The saved data supports tracking streaks and showing the user's questionnaire completion history.

Estimate: 1-3 weeks