feat: consume transactional email notifications

Add contract validation, SMTP delivery results, terminal failure context, neutral development seeding, and local Docker setup.

Ref: IT-1033

README.md

@@ -1,5 +1,98 @@
 # hrynco-notification-service
 
+## Documentation
+
+- [ItemTracker outbox email consumer](docs/itemtracker-outbox-email-consumer.md)
+
+## Development environment
+
+The development Docker Compose stack runs PostgreSQL, RabbitMQ, database migrations,
+the Notification Service Web and Worker applications, Seq, and Mailpit.
+
+Prerequisite: install and start Docker Desktop. Then run the installation script from
+the repository root:
+
+```powershell
+.\docker\environments\install-development.cmd
+```
+
+The script validates Docker and the Compose configuration, builds the application
+images, starts the complete stack in the background, and prints container status and
+the main development URLs. It can also be launched directly from File Explorer or
+from another working directory.
+
+To validate the setup without building images or creating containers, run:
+
+```powershell
+.\docker\environments\install-development.cmd --validate-only
+```
+
+By default, the script uses the tracked `docker/environments/.env.Development` file:
+
+```dotenv
+DB_NAME=notification_service
+DB_USER=postgres
+DB_PASS=postgres
+VOLUME_PREFIX=ns-dev
+RABBITMQ_USER=guest
+RABBITMQ_PASSWORD=guest
+RABBITMQ_AMQP_PORT=5672
+RABBITMQ_MANAGEMENT_PORT=15672
+WEB_PORT=5200
+DEVELOPMENT_EMAIL_SERVICE_NAME=TestService
+```
+
+To use personal values, copy it to the Git-ignored
+`docker/environments/.env.local`, adjust the values, and run Docker Compose manually:
+
+```powershell
+docker compose --env-file docker/environments/.env.local `
+  -f docker/environments/docker-compose.yml `
+  -f docker/environments/docker-compose.Development.yml `
+  up --build -d
+```
+
+After startup, the main development endpoints are:
+
+- Notification Service admin: `http://localhost:5200/admin/channels`
+- Notification templates: `http://localhost:5200/admin/templates`
+- RabbitMQ management: `http://localhost:15672` (`guest` / `guest`)
+- Mailpit inbox: `http://localhost:8025`
+- Seq logs: `http://localhost:5342`
+- PostgreSQL: `localhost:5433`
+
+During development migrations, the stack idempotently creates an active Mailpit SMTP
+channel and a neutral English `TestEmail` template for
+`DEVELOPMENT_EMAIL_SERVICE_NAME`. Existing channels and templates are never
+overwritten. Change that environment value when the publisher uses another service
+name.
+
+Check container status and follow Worker logs:
+
+```powershell
+docker compose --env-file docker/environments/.env.local `
+  -f docker/environments/docker-compose.yml `
+  -f docker/environments/docker-compose.Development.yml `
+  ps
+
+docker compose --env-file docker/environments/.env.local `
+  -f docker/environments/docker-compose.yml `
+  -f docker/environments/docker-compose.Development.yml `
+  logs -f worker
+```
+
+Stop the environment without deleting its database and RabbitMQ volumes:
+
+```powershell
+docker compose --env-file docker/environments/.env.local `
+  -f docker/environments/docker-compose.yml `
+  -f docker/environments/docker-compose.Development.yml `
+  down
+```
+
+See the [ItemTracker consumer guide](docs/itemtracker-outbox-email-consumer.md#local-end-to-end-setup)
+for the complete end-to-end setup.
+
 ## Notification worker flow
 
 ```mermaid
@@ -7,11 +100,15 @@ flowchart TD
     A[Worker host starts] --> B[Load config and register services]
     B --> C[Start SendEmailConsumer]
     C --> D[Receive message from notification.send-email]
-    D --> E[Resolve SendEmailService]
-    E --> F[Pick channel and template]
-    F --> G[Render email content]
-    G --> H[Send via SMTP]
-    H --> I[Update usage counters]
-    I --> J[Optionally publish result to reply queue]
-    H -. failure .-> K[Log and rethrow]
+    D --> E[Validate Notification.SendEmail.v1 metadata and payload]
+    E --> F[Resolve SendEmailService]
+    F --> G[Pick channel and exact-language template]
+    G --> H[Validate variables and render email content]
+    H --> I[Send via SMTP]
+    I --> J[Update usage counters]
+    J --> K[Optionally publish result to reply queue]
+    K --> L[Acknowledge RabbitMQ delivery]
+    I -. failure .-> M[Log and retry]
+    M -->|retries exhausted| N[Publish terminal failure result]
+    N --> O[Nack original delivery without requeue]
 ```