fix: add bin_location to inventory fixtures and service

- Add warehouse and bin_location fields to test fixtures
- Update InventoryService to include warehouse/bin_location when creating entries
- Fix all Inventory model instantiations in tests to include required fields
- All 119 inventory tests now pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/integration/api/v1/admin/test_inventory.py

@@ -452,6 +452,8 @@ class TestAdminInventoryAPI:
         new_inventory = Inventory(
             product_id=test_product.id,
             vendor_id=test_vendor.id,
+            warehouse="strassen",
+            bin_location="DEL-01-01",
             location="TO_DELETE_WAREHOUSE",
             quantity=50,
         )