Headless-first event calendar with month, week, day, N-day and agenda views, external CRUD contract, and a subscribable store.

Add the "Headless-first event calendar with month, week, day, N-day and agenda views, external CRUD contract, and a subscribable store." component (reui/event-calendar, from ReUI) to this project.

1. Run: npx get-ui-cli add reui/event-calendar --yes
2. Read the "Use it" snippet it prints, then import the component and render it where it fits.
3. Don't rewrite the installed file. Adapt it through its props and className, so `npx get-ui-cli update` can still merge upstream fixes.
4. Run: npx get-ui-cli doctor, and fix anything it reports.