Use selected day when creating new activity in UI

Fetch activities by selected day in UI

Make tab titles selectable by clicking in the UI

Set the default tab in TabBar to be the first tab

Fetch days from backend and show them in TabBar

Modify apiUrl to not include '/api/activities'

Add TabBar with placeholder data to frontend UI

Set up ESLint

Create TabBar component for frontend

Cache maven dependencies in ci.yml

Do not trigger ci.yml for frontend file changes

Fix indentation in frontend/App.tsx

Get day's activities with findByDayIdOrderByIndex

Return 404 from activity edit route if no such ID

Create "/api/days/{id}/activities" backend route