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/ScadaLink.ExternalSystemGateway.csproj

@@ -8,12 +8,20 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Data.SqlClient" Version="6.0.2" />
     <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="10.0.5" />
+    <PackageReference Include="Microsoft.Extensions.Http" Version="10.0.5" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.5" />
     <PackageReference Include="Microsoft.Extensions.Options" Version="10.0.5" />
   </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="../ScadaLink.Commons/ScadaLink.Commons.csproj" />
+    <ProjectReference Include="../ScadaLink.StoreAndForward/ScadaLink.StoreAndForward.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <InternalsVisibleTo Include="ScadaLink.ExternalSystemGateway.Tests" />
   </ItemGroup>
 
 </Project>