Add EmailAccountSyncWorker and configure EmailAccount entity

Introduced the `EmailAccountSyncWorker` background service to initialize and synchronize email accounts using RabbitMQ for event-driven processing. The service resolves email account configurations from application settings and upserts them into the repository.

Updated `MessagingServiceDbContext` to configure the `EmailAccount` entity, setting the `Username` property to use the `SQL_Latin1_General_CP1_CI_AS` collation for case-insensitive comparisons.

Added necessary `using` directives in `DependencyInjection.cs` to integrate new dependencies for AutoMapper, repositories, services, and background processing.

src/infrastructure/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -1,5 +1,7 @@
+using AutoMapper;
 using DigitalData.MessagingService.Application.Common.Interfaces;
 using DigitalData.MessagingService.Application.Common.Interfaces.Repositories;
+using DigitalData.MessagingService.Infrastructure.Mappings;
 using DigitalData.MessagingService.Infrastructure.Persistence;
 using DigitalData.MessagingService.Infrastructure.Queue;
 using DigitalData.MessagingService.Infrastructure.Repositories;

src/infrastructure/DigitalData.MessagingService.Infrastructure/Persistence/MessagingServiceDbContext.cs

@@ -16,6 +16,12 @@ public class MessagingServiceDbContext(DbContextOptions<MessagingServiceDbContex
     {
         base.OnModelCreating(modelBuilder);
 
+        modelBuilder.Entity<EmailAccount>(entity =>
+        {
+            entity.Property(e => e.Username)
+                  .UseCollation("SQL_Latin1_General_CP1_CI_AS");
+        });
+
         modelBuilder.Entity<ReceivedEmail>(entity =>
         {
             entity.HasMany(e => e.Attachments)

src/infrastructure/DigitalData.MessagingService.Infrastructure/Services/Background/EmailAccountSyncWorker.cs

@@ -0,0 +1,26 @@
+using DigitalData.MessagingService.Application.Common.Interfaces.Repositories;
+using DigitalData.MessagingService.Application.Common.Options;
+using DigitalData.MessagingService.Domain.Entities;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Options;
+
+namespace DigitalData.MessagingService.Infrastructure.Services.Background;
+
+/// <summary>
+/// A hosted background service responsible for initializing the competing email consumer pool.
+/// Leverages a push-based, event-driven RabbitMQ consumer to eliminate polling overhead.
+/// Email account configuration is resolved exclusively from application settings; no database access is performed.
+/// </summary>
+public class EmailAccountSyncWorker(IRepository<EmailAccount> Repository, IOptions<EmailAccountsOptions> Options) : BackgroundService
+{
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        foreach (var account in Options.Value.Accounts)
+        {
+            if (account is EmailAccount emailAccount)
+                await Repository.UpsertAsync(a => a.Username == emailAccount.Username, emailAccount, stoppingToken);
+        }
+
+        await Task.Delay(Timeout.Infinite, stoppingToken).ConfigureAwait(ConfigureAwaitOptions.SuppressThrowing);
+    }
+}