docs: extraction boundaries for Product, Identity and Order

[devin-ai-integration]

Summary

Contract the three remaining bounded-context extractions (Product, Identity, Order) are executed against, with the Customer extraction as the reference implementation.

The substance is the boundary-cutting rules, since that's where the monolith's EF graph (Customer 1—* Order 1—* OrderDetail *—1 Product, Order *—1 ApplicationUser) has to be severed:

• navigations become scalar IDs — Order.Customer → Order.CustomerId, OrderDetail.Product → OrderDetail.ProductId, Order.Cashier → Order.CashierId; Customer.Orders / Product.OrderDetails are deleted
• intra-context relations (Product ↔ ProductCategory, Product.Parent/Children, Order ↔ OrderDetail) stay as EF navigations
• enrichment is a best-effort HTTP call through the existing YARP routes on :5000, never a cross-database read; a failed lookup degrades the response instead of failing the request
• side effects go over RabbitMQ (OrderPlacedEvent), not service-to-service calls

Plus a per-service file allow-list: own src/Services/<Name> folder, additive-only Shared.Contracts, own compose env vars — gateway, Shared.Infrastructure, other services' folders and anything the in-flight Customer PR touches are off-limits (wait for that merge and rebase rather than copying).

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/25839f55096f4d6187d729c0a19f29f9
Open in Devin Desktop: https://partner-workshops.devinenterprise.com/desktop/session/25839f55096f4d6187d729c0a19f29f9?variant=devin
Requested by: @DhrovS

[devin-ai-integration]

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