Update Bot Inventory from Stock Events

[DakotaCondos]

As the Order API,
I want bot inventory in Cosmos DB to reflect stock changes published by the simulator,
so that order assignment can use a readable inventory view when selecting candidate bots.

Acceptance Criteria

• Given a RobotStockUpdated event is received
  When the event is processed
  Then the Function App updates the inventory section of the corresponding bot document.

• Given stock is reserved for an accepted or queued order
  When the stock update is processed
  Then quantity reserved and quantity available are updated in the bot document.

• Given a delivery is completed
  When the final stock update is processed
  Then quantity on hand, quantity reserved, and quantity available reflect the completed delivery.

• Given an inventory update event is older than the current inventory timestamp
  When the Function App processes the event
  Then the older event does not overwrite newer inventory values.