feat(notifications): config-gated Telegram anomaly alerts

- INotificationSink + AnomalyNotification (Application) and a testable
  GetPendingAnomalyNotificationsUseCase (date+score filter, event-title join,
  oldest-first). 4 use-case tests.
- TelegramNotificationSink posts to the Bot API via HttpClient (no SDK dependency);
  no-ops with a warning when unconfigured and never logs the token.
- AnomalyNotificationDispatcher BackgroundService: startup-baselined marker advanced
  past the newest sent (gap- and dup-free); idles until Notifications:Enabled.
- Wire options + named client + sink + dispatcher in InfrastructureModule. Add a
  secret-free Notifications section + steam-move tuning to appsettings.json
  (bot token + chat id go in appsettings.Local.json only).

src/Marathon.Infrastructure/InfrastructureModule.cs

@@ -1,5 +1,7 @@
+using Marathon.Application.Abstractions;
 using Marathon.Application.Configuration;
 using Marathon.Infrastructure.Configuration;
+using Marathon.Infrastructure.Notifications;
 using Marathon.Infrastructure.Persistence;
 using Marathon.Infrastructure.Scraping;
 using Marathon.Infrastructure.Workers;
@@ -50,11 +52,22 @@ public static class InfrastructureModule
             .AddOptions<ScrapingThrottle>()
             .Bind(config.GetSection(ScrapingThrottle.SectionName));
 
+        services
+            .AddOptions<NotificationOptions>()
+            .Bind(config.GetSection(NotificationOptions.SectionName));
+
         services.AddHostedService<UpcomingEventsPoller>();
         services.AddHostedService<LiveOddsPoller>();
         services.AddHostedService<ResultsWatchListPoller>();
         services.AddHostedService<AnomalyDetectionPoller>();
 
+        // Outbound anomaly notifications (Telegram). Sink + dispatcher are always
+        // registered; the dispatcher idles until Notifications:Enabled is true and
+        // the sink no-ops until a bot token + chat id are configured.
+        services.AddHttpClient(TelegramNotificationSink.HttpClientName);
+        services.AddSingleton<INotificationSink, TelegramNotificationSink>();
+        services.AddHostedService<AnomalyNotificationDispatcher>();
+
         return services;
     }
 }