Adjust inventory -- single or multi-item atomic (cycle count, shrinkage, revaluation)

ATOMIC-CREATE (2026-05-12): accepts items[] for multi-line atomic adjustments OR top-level product_id/quantity for single-item compat mode. All items adjust in one DB transaction; any failure rolls back all items (no partial writes). Positive or negative delta per item. Hard-blocks negative balance and zero-cost positives. GL: DR/CR Inventory + DR/CR Suspense or Shrinkage via glPostInventoryAdjustment, fires per item in same transaction (Rule 21). Connector: triggers async pushInventoryToMarketplaces. Response: {object:inventory_adjustment_result, items:[{index,product_id,balance,transaction,gl_amount,journal_entry_id,consumed_layers}], summary} for items[]; single object for compat mode. On failure: {error, code, hint, items_completed_before_failure} -- all items rolled back regardless of items_completed_before_failure. migration:write scope: documents authorization for opening-balance loads. Hard-blocks still apply.