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/unit/services/test_stats_service.py

@@ -533,6 +533,8 @@ class TestStatsService:
         unique_id = str(uuid.uuid4())[:8]
         additional_inventory = Inventory(
             gtin=f"123456789{unique_id[:4]}",
+            warehouse="strassen",
+            bin_location=f"ST-{unique_id[:2]}-01",
             location=f"LOCATION2_{unique_id}",
             quantity=25,
             reserved_quantity=5,