Synchronous bulk exports cause memory exhaustion and timeout

Serving complete dataset exports as synchronous API responses loads millions of rows into memory at once. Django loads entire queryset into memory before iteration without iterator(). Causes OOM and 90+ second response times that exceed client timeouts.

Implement async export pattern: return HTTP 202 Accepted immediately, queue Celery background task using iterator(chunk_size=1000) to stream rows in 1000-row batches keeping memory flat, write to CSV/file, upload to storage, send email with download link when complete. Never serve full dataset as synchronous response.