Phase 3A: Site runtime foundation — Akka cluster, SQLite persistence, Deployment Manager singleton, Instance Actor

- WP-1: Site cluster config (keep-oldest SBR, down-if-alone, 2s/10s failure detection)
- WP-2: Site-role host bootstrap (no Kestrel, SQLite paths)
- WP-3: SiteStorageService with deployed_configurations + static_attribute_overrides tables
- WP-4: DeploymentManagerActor as cluster singleton with staggered Instance Actor creation,
  OneForOneStrategy/Resume supervision, deploy/disable/enable/delete lifecycle
- WP-5: InstanceActor with attribute state, GetAttribute/SetAttribute, SQLite override persistence
- WP-6: CoordinatedShutdown verified for graceful singleton handover
- WP-7: Dual-node recovery (both seed nodes, min-nr-of-members=1)
- WP-8: 31 tests (storage CRUD, actor lifecycle, supervision, negative checks)
389 total tests pass, zero warnings.

src/ScadaLink.SiteRuntime/ServiceCollectionExtensions.cs

@@ -1,18 +1,43 @@
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using ScadaLink.SiteRuntime.Persistence;
 
 namespace ScadaLink.SiteRuntime;
 
 public static class ServiceCollectionExtensions
 {
+    /// <summary>
+    /// Registers Site Runtime services including SiteStorageService for SQLite persistence.
+    /// The caller must register an <see cref="ISiteStorageConnectionProvider"/> or call the
+    /// overload with an explicit connection string.
+    /// </summary>
     public static IServiceCollection AddSiteRuntime(this IServiceCollection services)
     {
-        // Phase 0: skeleton only
+        // SiteStorageService is registered by the Host using AddSiteRuntime(connectionString)
+        // This overload is for backward compatibility / skeleton placeholder
+        return services;
+    }
+
+    /// <summary>
+    /// Registers Site Runtime services with an explicit SQLite connection string.
+    /// </summary>
+    public static IServiceCollection AddSiteRuntime(this IServiceCollection services, string siteDbConnectionString)
+    {
+        services.AddSingleton(sp =>
+        {
+            var logger = sp.GetRequiredService<ILogger<SiteStorageService>>();
+            return new SiteStorageService(siteDbConnectionString, logger);
+        });
+
+        services.AddHostedService<SiteStorageInitializer>();
+
         return services;
     }
 
     public static IServiceCollection AddSiteRuntimeActors(this IServiceCollection services)
     {
-        // Phase 0: placeholder for Akka actor registration
+        // Actor registration is handled by AkkaHostedService.RegisterSiteActors()
+        // which creates the DeploymentManager singleton and proxy
         return services;
     }
 }