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>

HrynCo.NotificationService.DAL.Abstract/Repositories/IEmailChannelRepository.cs

@@ -7,6 +7,7 @@ public interface IEmailChannelRepository
     Task<IReadOnlyList<EmailChannel>> GetAllAsync(CancellationToken ct = default);
     Task<IReadOnlyList<EmailChannel>> GetByServiceAsync(string serviceName, CancellationToken ct = default);
     Task<EmailChannel?> GetByIdAsync(Guid id, CancellationToken ct = default);
+    Task<IReadOnlyList<ChannelWithUsage>> GetAllWithUsageSummaryAsync(DateOnly today, CancellationToken ct = default);
     Task AddAsync(EmailChannel channel, CancellationToken ct = default);
     Task UpdateAsync(EmailChannel channel, CancellationToken ct = default);
     Task DeleteAsync(EmailChannel channel, CancellationToken ct = default);

HrynCo.NotificationService.DAL.Abstract/Repositories/IEmailChannelUsageRepository.cs

@@ -1,5 +1,3 @@
-using HrynCo.NotificationService.DAL.Abstract.Providers;
-
 namespace HrynCo.NotificationService.DAL.Abstract.Repositories;
 
 public interface IEmailChannelUsageRepository