Implement notifications service with shared messaging and email drivers (#36)

backend/README.md

@@ -12,6 +12,8 @@ backend/
 │   ├── auth/                Login/protected HTTP routes, DTOs and configuration
 │   ├── sessions/            Session models, refresh storage, cookies and tokens
 │   └── verification/        Verification models, configuration and storage
+├── notifications/           Internal gRPC notification service and email workers
+│   └── interface/           Independent protobuf/client contract module
 └── shared/                  Reusable library module
     ├── go.mod
     ├── database/            Connection, transactions and repository primitives
@@ -27,9 +29,11 @@ not implemented by this customer-BFF bootstrap. Shared infrastructure has no
 local `replace` for `../shared`; each module has its own dependency manifest.
 
 Run the product with `make run-backend`; see its [run guide](product/README.md).
-`make test` runs both backend modules and the frontend. `make lint-backend` checks
-both Go modules and their architecture boundaries.
+`make test` runs all backend modules and the frontend. `make lint-backend` checks
+all Go modules and their architecture boundaries.
 
 Copied source remains locally owned. See [provenance](PROVENANCE.md), the
 [architecture/API plan](../docs/architecture/bff.md) and the
 [delivery record](../docs/implementation.md).
+
+Notifications uses shared database and messaging infrastructure. See its [run guide](notifications/README.md) and [protobuf interface](notifications/interface/proto/v1/interface.proto). Generated client bindings are ignored; Make generates them before backend checks.