feat(esg): TimeoutSeconds travels the artifact pipeline (additive contract) into site SQLite so site-side calls honor it

Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj

tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Repositories/SiteRepositoryTests.cs

@@ -54,6 +54,26 @@ public class SiteRepositoryTests : IDisposable
         Assert.Equal("https://api.example.com", all[0].EndpointUrl);
     }
 
+    /// <summary>
+    /// ExternalSystemGateway (Timeout): the per-system <c>TimeoutSeconds</c> stored via
+    /// <see cref="SiteStorageService.StoreExternalSystemAsync"/> must round-trip through the
+    /// site SQLite store and back out via the repository, so site-side calls honor it.
+    /// </summary>
+    [Fact]
+    public async Task SiteStorage_ExternalSystem_TimeoutSeconds_RoundTrips()
+    {
+        var storage = NewStorage();
+        await storage.InitializeAsync();
+        await storage.StoreExternalSystemAsync(
+            "WeatherApi", "https://api.example.com", "ApiKey", "{\"key\":\"x\"}", null, 7);
+
+        var repo = new SiteExternalSystemRepository(storage);
+        var found = await repo.GetExternalSystemByNameAsync("WeatherApi");
+
+        Assert.NotNull(found);
+        Assert.Equal(7, found!.TimeoutSeconds);
+    }
+
     /// <summary>
     /// SiteRuntime-007: the synthetic ID for an external system must be identical when
     /// the storage service and repository are re-created (simulating a process restart).