feat: add CRUD endpoints for events

[nadavosa]

Summary

Coordinators need to create and manage events from the dashboard, which then appear on the public-facing event page. New endpoints are needed to support this.

Required endpoints

• POST /event — create an event (headline, description, date, time, location, registration link)
• GET /event — list all active events (used by public website)
• PATCH /event/:id — update an event
• DELETE /event/:id — delete/deactivate an event

Relates to

need4deed-org/fe#361

Acceptance criteria

• Full CRUD for events is available
• GET /event is publicly accessible (no auth required)
• Create/update/delete require coordinator auth