Added missing helper functions for all purchase order reasoning types:
- create_po_reasoning_supplier_contract: Contract-based orders
- create_po_reasoning_safety_stock: Safety stock replenishment
- create_po_reasoning_seasonal_demand: Seasonal preparation
- create_po_reasoning_production_requirement: Production needs
- create_po_reasoning_manual_request: Manual orders
These functions generate structured reasoning_data for i18n translation
and provide consistent reasoning structure across all PO types.
Fixes ImportError in demo-seed-purchase-orders pod.
0a2982d22f