scan_directory walks ImportSettings.import_scan_path, creates an
ImportBatch, enumerates supported files into ImportTasks, and enqueues
import_media_file per task. import_media_file moves the task through
its state machine (pending → queued → processing → complete/skipped/failed),
updates ImportBatch counters atomically (UPDATE ... SET col = col + 1),
enqueues a thumbnail task on success, and marks the batch complete when
the last task drains.
generate_thumbnail runs on its own queue (thumbnail) so big imports
don't starve thumbnail throughput; failure here is logged and does not
fail the import.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
bvandeusen