Phase 8: Production readiness — failover tests, security hardening, sandboxing, deployment docs

- WP-1-3: Central/site failover + dual-node recovery tests (17 tests)
- WP-4: Performance testing framework for target scale (7 tests)
- WP-5: Security hardening (LDAPS, JWT key length, no secrets in logs) (11 tests)
- WP-6: Script sandboxing adversarial tests (28 tests, all forbidden APIs)
- WP-7: Recovery drill test scaffolds (5 tests)
- WP-8: Observability validation (structured logs, correlation IDs, metrics) (6 tests)
- WP-9: Message contract compatibility (forward/backward compat) (18 tests)
- WP-10: Deployment packaging (installation guide, production checklist, topology)
- WP-11: Operational runbooks (failover, troubleshooting, maintenance)
92 new tests, all passing. Zero warnings.

src/ScadaLink.ExternalSystemGateway/ServiceCollectionExtensions.cs

@@ -1,4 +1,5 @@
 using Microsoft.Extensions.DependencyInjection;
+using ScadaLink.Commons.Interfaces.Services;
 
 namespace ScadaLink.ExternalSystemGateway;
 
@@ -6,13 +7,22 @@ public static class ServiceCollectionExtensions
 {
     public static IServiceCollection AddExternalSystemGateway(this IServiceCollection services)
     {
-        // Phase 0: skeleton only
+        services.AddOptions<ExternalSystemGatewayOptions>()
+            .BindConfiguration("ScadaLink:ExternalSystemGateway");
+
+        services.AddHttpClient();
+        services.AddSingleton<ExternalSystemClient>();
+        services.AddSingleton<IExternalSystemClient>(sp => sp.GetRequiredService<ExternalSystemClient>());
+        services.AddSingleton<DatabaseGateway>();
+        services.AddSingleton<IDatabaseGateway>(sp => sp.GetRequiredService<DatabaseGateway>());
+
         return services;
     }
 
     public static IServiceCollection AddExternalSystemGatewayActors(this IServiceCollection services)
     {
-        // Phase 0: placeholder for Akka actor registration
+        // WP-10: Actor registration happens in AkkaHostedService.
+        // Script Execution Actors run on dedicated blocking I/O dispatcher.
         return services;
     }
 }