Includes Cards/Sleeves/Emblems/LeaderSkins/Degrees/MyPageBackgrounds/Items
under AsSplitQuery, plus caller-supplied extras via InventoryLoadConfig.
Opens a DB transaction and returns an InventoryTransaction shell. All
mutation methods throw NotImplementedException until subsequent tasks
land them.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
