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);

HrynCo.NotificationService.Services/EmailChannels/Send/SendEmailCommand.cs

@@ -0,0 +1,17 @@
+using HrynCo.NotificationService.Services.Core;
+using MediatR;
+
+namespace HrynCo.NotificationService.Services.EmailChannels.Send;
+
+/// <summary>
+/// Sends an email via the channel associated with the given channel ID,
+/// then increments the usage counter for that channel.
+/// </summary>
+public sealed record SendEmailCommand(
+    Guid ChannelId,
+    string RecipientEmail,
+    string RecipientName,
+    string Subject,
+    string HtmlBody,
+    string? TextBody
+) : IRequest<ServiceResult<Core.Unit>>;

HrynCo.NotificationService.Services/EmailChannels/Send/SendEmailHandler.cs

@@ -0,0 +1,80 @@
+using System.Net;
+using System.Net.Mail;
+using HrynCo.NotificationService.DAL.Abstract;
+using HrynCo.NotificationService.DAL.Abstract.Providers;
+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.Send;
+
+internal sealed class SendEmailHandler
+    : RequestHandler<SendEmailCommand, ServiceResult<Core.Unit>>
+{
+    private readonly IEmailChannelRepository _channels;
+    private readonly IEmailChannelUsageRepository _usage;
+
+    public SendEmailHandler(
+        IContextualSerilogLogger<SendEmailCommand> logger,
+        IUnitOfWork unitOfWork,
+        IEmailChannelRepository channels,
+        IEmailChannelUsageRepository usage)
+        : base(logger, unitOfWork)
+    {
+        _channels = channels;
+        _usage = usage;
+    }
+
+    protected override async Task<ServiceResult<Core.Unit>> DoOnHandle(
+        SendEmailCommand request, CancellationToken cancellationToken)
+    {
+        var channel = await _channels.GetByIdAsync(request.ChannelId, cancellationToken);
+        if (channel is null)
+            return Failure<Core.Unit>($"Channel '{request.ChannelId}' not found.");
+
+        if (channel.Settings is not SmtpChannelSettings smtp)
+            return Failure<Core.Unit>($"Channel type '{channel.EmailChannelType}' is not supported for sending.");
+
+        try
+        {
+            using var client = new SmtpClient(smtp.Host, smtp.Port)
+            {
+                EnableSsl = smtp.UseSsl,
+                Credentials = string.IsNullOrWhiteSpace(smtp.Username)
+                    ? null
+                    : new NetworkCredential(smtp.Username, smtp.Password)
+            };
+
+            using var mail = new MailMessage
+            {
+                From = new MailAddress(smtp.FromEmail, smtp.FromName),
+                Subject = request.Subject,
+                Body = request.HtmlBody,
+                IsBodyHtml = true
+            };
+
+            if (!string.IsNullOrWhiteSpace(request.TextBody))
+            {
+                var plain = AlternateView.CreateAlternateViewFromString(request.TextBody, null, "text/plain");
+                mail.AlternateViews.Add(plain);
+            }
+
+            mail.To.Add(new MailAddress(request.RecipientEmail, request.RecipientName));
+
+            await client.SendMailAsync(mail, cancellationToken);
+        }
+        catch (Exception ex)
+        {
+            Logger.Error(ex, "SMTP send failed for channel {ChannelId}", request.ChannelId);
+            return Failure<Core.Unit>(ex.Message);
+        }
+
+        await _usage.IncrementUsageAsync(
+            request.ChannelId,
+            DateOnly.FromDateTime(DateTime.UtcNow),
+            cancellationToken);
+
+        return Success(Unit.Value);
+    }
+}