T4(customer): fix gateway route transform to map /api/customers → /api/customer

[devin-ai-integration]

Summary

The YARP gateway strips /api/customers via PathRemovePrefix, but the Customer service controller listens at api/customer (singular). Requests like GET /api/customers became GET / and 404'd.

Added a PathPrefix transform so the route pipeline becomes:

PathRemovePrefix: "/api/customers"  →  PathPrefix: "/api/customer"

Example flows:

• GET /api/customers → / → /api/customer (list endpoint)
• GET /api/customers/5 → /5 → /api/customer/5 (get-by-id)
• POST /api/customers → / → /api/customer (create)

Only src/ApiGateway/appsettings.json changed.

Part of the Customer microservice carve-out stacked PR chain (T4/T5).

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/df4fd98794c34738bf5a70c588276dcb
Requested by: @mbatchelor81

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[devin-ai-integration]

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[devin-ai-integration]

Devin Review found 1 potential issue.

[devin-ai-integration]

🚩 Other service routes have the same prefix-stripping problem that this PR fixes only for the customer route

This PR adds PathPrefix: /api/customer to fix routing for the customer service, which uses [Route("api/[controller]")] resolving to api/Customer. However, the identity, order, product, and notification routes all have the identical issue: they strip /api/{service} via PathRemovePrefix but never re-add the controller prefix. For example, the order route strips /api/orders so /api/orders/5 becomes /5, which is forwarded to http://order-service:5003/5 — but the OrderController at src/Services/Order/Order.API/Controllers/OrderController.cs:6 expects api/Order/5. The same applies to IdentityController (src/Services/Identity/Identity.API/Controllers/IdentityController.cs:6), ProductController (src/Services/Product/Product.API/Controllers/ProductController.cs:6), and NotificationController (src/Services/Notification/Notification.API/Controllers/NotificationController.cs:9). These are pre-existing issues but this PR establishes the fix pattern — the other routes should likely get the same treatment.

(Refers to lines 24-28)

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[devin-ai-integration]

Agreed — the other routes (identity, order, product, notification) have the same prefix-stripping gap. This PR is intentionally scoped to only the customer route per the task spec; fixing the others would be a separate follow-up.