- Add consumer_group_id to sale.order for tracking the consumer group
- Fix stock.picking consumer_group_id to use sale_id.consumer_group_id
- Add group_ids inverse relation in res.partner for bidirectional access
- Remove auto-calculation of consumer_group_id, data comes directly from group_order.group_ids[0]
- Add debug logging for consumer_group propagation
- commitment_date propagates directly from group_order (no recalculation)
