feat: consume transactional email notifications

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

Ref: IT-1033

docker/environments/docker-compose.Development.yml

@@ -3,7 +3,9 @@ name: hrynco-notification-service
 services:
   migrator:
     environment:
+      - DOTNET_ENVIRONMENT=Development
       - App__ConnectionString=Host=db;Port=5432;Database=notification_service;Username=postgres;Password=postgres
+      - DevelopmentSeed__ServiceName=${DEVELOPMENT_EMAIL_SERVICE_NAME:-TestService}
 
   web:
     environment:
@@ -29,9 +31,6 @@ services:
     environment:
       RABBITMQ_DEFAULT_USER: guest
       RABBITMQ_DEFAULT_PASS: guest
-    ports:
-      - "5672:5672"
-      - "15672:15672"
     networks:
       - internal
 
@@ -55,10 +54,17 @@ services:
     networks:
       - internal
 
+  mailpit:
+    image: axllent/mailpit:v1.30.0
+    ports:
+      - "8025:8025"
+    networks:
+      - internal
+
 volumes:
   pgdata:
     name: ns-dev-pgdata
   rabbitmq_data:
     name: ns-dev-rabbitmq-data
   seq_data:
-    name: ns-dev-seq
+    name: ns-dev-seq