Add Inventory Transfer: stock transfers and draft purchase orders

Adds InventoryTransferPage covering stock transfer between NLD and GO HUNTER in both directions, plus the Draft Purchase Order flow, and registers it on ProductsManager.

Four new cases in tests/InventoryTransfer.spec.ts (TC-NLD-TRANSFER-001..004) with inputs in test-data/inventoryTransferData.json.

Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com