Event Registration Platform

Problem/Feature Description

A community center needs a Flask API for managing events and registrations. They host workshops, meetups, and classes. The API should handle events (title, description, date, max_attendees, location) and registrations (attendee_name, attendee_email, event_id, registered_at).

Requirements:

1. Create, list, and get events.
2. Register attendees for an event -- reject if the event is full (registrations >= max_attendees).
3. List registrations for a specific event.
4. Cancel a registration (DELETE).
5. A GET /api/events?upcoming=true filter to show only future events.
6. Each request should have a unique request ID (X-Request-ID header), generated if not provided by the client, and returned in the response.
7. All timestamps should be ISO 8601 format.
8. Proper logging -- each request should be logged with its request ID.

The system should be well-structured so that a junior developer can understand and extend it.

Output Specification

Produce Python source files in a event-platform/ directory:

• app/__init__.py -- application factory
• app/extensions.py -- extension instances
• app/errors.py -- custom exceptions and error handlers
• app/db.py -- data store (in-memory or SQLite)
• app/routes/events.py -- events blueprint
• app/routes/registrations.py -- registrations blueprint
• tests/conftest.py -- test fixtures
• run.py -- entry point
• requirements.txt

Do not run pip install or start the server.