fix(host): resolve Host-003,004 — replace plaintext secrets with env placeholders, validate site seed-node ports; re-triage Host-002

tests/ScadaLink.Host.Tests/HealthCheckTests.cs

@@ -11,6 +11,12 @@ public class HealthCheckTests : IDisposable
 {
     private readonly List<IDisposable> _disposables = new();
 
+    public HealthCheckTests()
+    {
+        // Host-003: connection strings are externalised; supply them via env vars.
+        _disposables.Add(new CentralDbTestEnvironment());
+    }
+
     public void Dispose()
     {
         foreach (var d in _disposables)