Feature: Join / leave events

Summary

Users can attend or leave an event; attendee count reflected.

User story

As a user, I want to join or leave events so my plans are tracked.

Scope

• Backend: POST /events/:id/attend, POST /events/:id/unattend, GET /me/attending.
• Prevent duplicate attend; handle not attending on unattend.
• Frontend: buttons on event page; “My attending” page.

Tasks

• Endpoints + controller logic.
• Tests (happy + edge cases).
• Frontend buttons, attending view, optimistic UI.
• Update documentation.

Acceptance criteria

• Authenticated user can attend once; duplicate returns 400.
• Unattend removes user; not attending returns 400 or no-op (decide & document).
• “My attending” lists only events the user joined.

Test notes

• 401 when unauthenticated; 404 when event not found.

Dependencies

• Depends on: “Secure authentication via JWT”.
• Relates to: “Create, update, delete, and list events”.