Implement detect_objects Celery task: - Runs YOLOv8n on 640px thumbnail via ONNX Runtime - Creates Tag(kind=object) rows for each COCO class detected - Writes photo_tags associations with confidence, bbox, and source - Wipes previous detections per source model on re-run No new tables/migrations — uses the unified Tag model from PR3. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>