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.Services/EmailChannels/GetUsageSummary/GetChannelUsageSummaryHandler.cs

@@ -0,0 +1,45 @@
+using HrynCo.NotificationService.DAL.Abstract;
+using HrynCo.NotificationService.DAL.Abstract.Repositories;
+using HrynCo.NotificationService.Services.Core;
+using HrynCo.NotificationService.Services.Logging;
+using static HrynCo.NotificationService.Services.Core.ServiceResultHelper;
+
+namespace HrynCo.NotificationService.Services.EmailChannels.GetUsageSummary;
+
+internal sealed class GetChannelUsageSummaryHandler
+    : RequestHandler<GetChannelUsageSummaryQuery, ServiceResult<IReadOnlyList<ChannelUsageEntry>>>
+{
+    private readonly IEmailChannelRepository _channelsRepository;
+
+    public GetChannelUsageSummaryHandler(
+        IContextualSerilogLogger<GetChannelUsageSummaryQuery> logger,
+        IUnitOfWork unitOfWork,
+        IEmailChannelRepository channelsRepository)
+        : base(logger, unitOfWork)
+    {
+        _channelsRepository = channelsRepository;
+    }
+
+    protected override async Task<ServiceResult<IReadOnlyList<ChannelUsageEntry>>> DoOnHandle(
+        GetChannelUsageSummaryQuery request, CancellationToken cancellationToken)
+    {
+        var today = DateOnly.FromDateTime(DateTime.UtcNow);
+
+        var rows = await _channelsRepository.GetAllWithUsageSummaryAsync(today, cancellationToken);
+
+        var entries = rows
+            .Select(r => new ChannelUsageEntry(
+                ChannelId:    r.Channel.Id,
+                ServiceName:  r.Channel.ServiceName,
+                ChannelType:  r.Channel.EmailChannelType.ToString(),
+                IsActive:     r.Channel.IsActive,
+                Priority:     r.Channel.Priority,
+                DailyLimit:   r.Channel.DailyLimit,
+                MonthlyLimit: r.Channel.MonthlyLimit,
+                DailySent:    r.DailySent,
+                MonthlySent:  r.MonthlySent))
+            .ToList();
+
+        return Success<IReadOnlyList<ChannelUsageEntry>>(entries);
+    }
+}

HrynCo.NotificationService.Services/EmailChannels/GetUsageSummary/GetChannelUsageSummaryQuery.cs

@@ -0,0 +1,19 @@
+using HrynCo.NotificationService.DAL.Abstract.Providers;
+using HrynCo.NotificationService.Services.Core;
+using MediatR;
+
+namespace HrynCo.NotificationService.Services.EmailChannels.GetUsageSummary;
+
+public sealed record GetChannelUsageSummaryQuery
+    : IRequest<ServiceResult<IReadOnlyList<ChannelUsageEntry>>>;
+
+public sealed record ChannelUsageEntry(
+    Guid ChannelId,
+    string ServiceName,
+    string ChannelType,
+    bool IsActive,
+    int Priority,
+    int? DailyLimit,
+    int? MonthlyLimit,
+    int DailySent,
+    int MonthlySent);