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.EF/Repositories/EmailChannelRepository.cs

@@ -35,6 +35,30 @@ internal sealed class EmailChannelRepository : EfRepository<EmailChannelEntity>,
         return entities.Select(MapToDomain).ToList();
     }
 
+    public async Task<IReadOnlyList<ChannelWithUsage>> GetAllWithUsageSummaryAsync(
+        DateOnly today, CancellationToken ct = default)
+    {
+        var rows = await DbSet
+            .AsNoTracking()
+            .OrderBy(c => c.ServiceName)
+            .ThenBy(c => c.Priority)
+            .Select(c => new
+            {
+                Channel = c,
+                DailySent = c.UsageRecords
+                    .Where(u => u.Date == today)
+                    .Sum(u => (int?)u.SentCount) ?? 0,
+                MonthlySent = c.UsageRecords
+                    .Where(u => u.Date.Year == today.Year && u.Date.Month == today.Month)
+                    .Sum(u => (int?)u.SentCount) ?? 0
+            })
+            .ToListAsync(ct);
+
+        return rows
+            .Select(r => new ChannelWithUsage(MapToDomain(r.Channel), r.DailySent, r.MonthlySent))
+            .ToList();
+    }
+
     public async Task<EmailChannel?> GetByIdAsync(Guid id, CancellationToken ct = default)
     {
         EmailChannelEntity? entity = await DbSet.AsNoTracking().FirstOrDefaultAsync(x => x.Id == id, ct);