Extract Product bounded context into the Product service

[devin-ai-integration]

Summary

Extracts the Product bounded context out of quickapp-monolith into a self-contained service under src/Services/Product, per docs/extraction-boundaries.md (PR #87).

• Domain: Product / ProductCategory ported from QuickApp.Core/Models/Shop/. Intra-context navigations kept (Product ↔ ProductCategory, Product.Parent/Children); the cross-context Product.OrderDetails navigation is dropped — order lines reference products by ProductId only.
• Infrastructure: ProductDbContext now maps AppProducts / AppProductCategories with the monolith's column constraints (Name(100), Description(500), Icon(256), prices decimal(18,2), parent Restrict, category Cascade) and stamps audit fields in SaveChanges(Async). EF Core migration InitialProductSchema + EF-backed repositories + an idempotent ProductDbSeeder (categories None/Cars, products BMW M6 / Nissan Patrol / one uncategorised sample) so the gateway returns rows on a fresh volume.
• API: full CRUD the monolith never had — GET|POST /api/products, GET|PUT|DELETE /api/products/{id} and the same set under /api/products/categories. Wire shape stays ProductVM-compatible (incl. flattened productCategoryName), plus parentId/productCategoryId which CRUD needs for assignment. Creating/updating a product with an unknown productCategoryId returns 400.
• Startup retries migrate+seed (10 × 3s) because compose depends_on does not wait for Postgres readiness:

for (var attempt = 1; ; attempt++)
    try { await db.Database.MigrateAsync(); await ProductDbSeeder.SeedAsync(db); break; }
    catch (Exception ex) when (attempt < maxAttempts) { /* log + delay 3s */ }

• Tests: Product.Tests (16 tests) over WebApplicationFactory, covering the read path and every CRUD verb for products and categories plus seeder idempotency. ProductDatabaseFixture starts a Testcontainers Postgres and falls back to the EF in-memory provider when Docker is unavailable.

No changes to src/ApiGateway/** — the existing YARP route /api/products/{**catch-all} → http://product-service:5004/ already works.

Verification

dotnet build Services/Product/Product.API/Product.API.csproj -c Release → 0 warnings, 0 errors.
dotnet test Services/Product/Product.Tests/Product.Tests.csproj -c Release → Passed! Failed: 0, Passed: 16, Skipped: 0.

Through the gateway on port 5000 (compose stack):

$ curl -s -i http://localhost:5000/api/products
HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Server: Kestrel

[{"id":1,"name":"BMW M6","description":"Yet another masterpiece from the world's best car manufacturer","icon":null,"buyingPrice":109775.00,"sellingPrice":114234.00,"unitsInStock":12,"isActive":true,"isDiscontinued":false,"parentId":null,"productCategoryId":2,"productCategoryName":"Cars"},
 {"id":2,"name":"Nissan Patrol",...,"productCategoryName":"Cars"},
 {"id":3,"name":"Uncategorised sample",...,"productCategoryName":"None"}]

$ curl -s -o /dev/null -w "%{http_code}\n" http://localhost:5000/api/products/1
200
$ curl -s -X POST http://localhost:5000/api/products -H 'Content-Type: application/json' \
    -d '{"name":"Audi RS7","buyingPrice":95000,"sellingPrice":105000,"unitsInStock":3,"isActive":true,"isDiscontinued":false,"productCategoryId":2}'
201 {"id":4,"name":"Audi RS7",...,"productCategoryName":"Cars"}
$ curl -s -X PUT http://localhost:5000/api/products/4 -H 'Content-Type: application/json' -d '{...,"name":"Audi RS7 Sportback",...}'
200 {"id":4,"name":"Audi RS7 Sportback",...}
$ curl -s -o /dev/null -w "%{http_code}\n" -X DELETE http://localhost:5000/api/products/4
204
$ curl -s http://localhost:5000/api/products/categories
200 [{"id":2,"name":"Cars",...},{"id":1,"name":"None",...}]

Notes / known issues

• docker compose -f src/docker-compose.yml up --build cannot boot the whole stack on main: notification-service fails to build because Notification.API.csproj references ..\..\Shared\... instead of ..\..\..\Shared\... (pre-existing, out of this PR's allowed scope — flagged as the boundaries doc requires). Everything else (postgres, rabbitmq, identity, customer, order, product, api-gateway) builds and boots, and the curl evidence above was captured against that stack.
• Expected trivial conflicts with the Customer extraction (Extract Customer bounded context into the Customer service #88), to be resolved by rebasing onto main after it merges: src/Microservices.sln (this PR only adds Product.Tests) and the one-line <ProjectReference> path fix in src/Services/Product/Product.API/Product.API.csproj (..\..\Shared → ..\..\..\Shared), which this build needs.

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/ac94963abb93407fb387a85677193555
Open in Devin Desktop: https://partner-workshops.devinenterprise.com/desktop/session/ac94963abb93407fb387a85677193555?variant=devin
Requested by: @DhrovS

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