feat: add RabbitMQ worker, contracts, usage UI in channels screen

- Add HrynCo.NotificationService.Contracts project with SendEmailMessage and NotificationResultMessage
- Add SendEmailConsumer (RabbitMQ worker) with reply-to pattern via CorrelationContext.ReplyTo
- Add SendEmailHandler owning SMTP send + usage increment as business logic
- Add GetChannelUsageSummaryHandler with single DB query via navigation property
- Merge usage stats inline into channels list (daily/monthly with progress bars)
- Refactor AdminChannelsController.Index to use GetChannelUsageSummaryQuery
- Add RabbitMQ service to docker-compose files
- Remove dead AdminChannelUsageController, ChannelUsageViewModel, ChannelUsageSummary

Ref: IT-628

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

docker/environments/docker-compose.Development.yml

@@ -1,3 +1,5 @@
+name: hrynco-notification-service
+
 services:
   migrator:
     environment:
@@ -15,7 +17,29 @@ services:
     environment:
       - DOTNET_ENVIRONMENT=Development
       - App__ConnectionString=Host=db;Port=5432;Database=notification_service;Username=postgres;Password=postgres
+      - App__RabbitMq__Host=rabbitmq
+      - App__RabbitMq__User=guest
+      - App__RabbitMq__Password=guest
       - Serilog__WriteTo__1__Args__serverUrl=http://seq
+    depends_on:
+      rabbitmq:
+        condition: service_healthy
+
+  rabbitmq:
+    image: rabbitmq:4-management-alpine
+    environment:
+      RABBITMQ_DEFAULT_USER: guest
+      RABBITMQ_DEFAULT_PASS: guest
+    ports:
+      - "5672:5672"
+      - "15672:15672"
+    healthcheck:
+      test: ["CMD", "rabbitmq-diagnostics", "ping"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+    volumes:
+      - notification_rabbitmq:/var/lib/rabbitmq
 
   db:
     image: postgres:17
@@ -40,4 +64,5 @@ services:
 
 volumes:
   notification_db:
-  notification_seq:
+  notification_seq:
+  notification_rabbitmq: