Extends the data_import_batches collection for the PO/DN async-import
queue redesign (see spec docs/superpowers/specs/2026-08-19-po-import-queue-redesign.md
and plan docs/superpowers/plans/2026-08-19-po-import-queue-implementation.md).
Adds 8 fields:
content_type, status (select: pending|processing|processed|failed|dead),
attempts, last_error, last_attempt_at, next_retry_at, processed_at,
processed_record_id
Extends the batch_type enum to include purchase_orders and delivery_notes.
Adds index idx_batches_pending on (status, batch_type, next_retry_at) for
the cron query.
Idempotent: safe to re-run.
Co-Authored-By: Claude <noreply@anthropic.com>
c534572590