Blocking synchronous OpenAI calls inside Event.save() cause request latency and failures

## Describe the bug

The `Event.save()` method performs **synchronous OpenAI API calls** via `generate_suggested_location()` and `generate_summary()`.
These methods instantiate `OpenAi` and call `complete()` during the model save lifecycle, causing the request handling thread/worker to block until the external API responds.

This introduces significant latency and makes event creation or updates tightly coupled to OpenAI availability and response time.

---

## To Reproduce

1. Create or update an `Event` instance that triggers `Event.save()`.
2. Ensure `generate_suggested_location()` and/or `generate_summary()` are executed.
3. Observe the request duration while the OpenAI API call is in progress.
4. If the OpenAI API is slow or unavailable, the request blocks or fails.

---

## Expected behavior

Saving an `Event` should be fast and non-blocking.
AI-generated fields (summary, suggested location) should be computed asynchronously or via a background task, so that:

- Event creation/update does not block on external API calls
- Temporary OpenAI outages do not break core functionality
- Request latency remains predictable

---

## Are you going to work on fixing this?

- [x] Yes
- [ ] No

---

## Screenshots

Not applicable (backend performance/reliability issue).

---

## Desktop

- OS: N/A
- Browser: N/A
- Version: N/A

---

## Smartphone

- Device: N/A
- OS: N/A
- Browser: N/A
- Version: N/A

---

## Additional context

The synchronous OpenAI calls occur inside a Django model `save()` method, which is part of the critical request path.
Offloading these operations to a background task queue (e.g., Celery) or triggering them asynchronously after persistence would significantly improve performance and reliability.