Phase 0 WP-0.1: Create .NET 10 solution structure with all 17 component projects

17 source projects (Commons + Host + 15 components) and 17 xUnit test projects.
SLNX format, net10.0, nullable enabled, warnings as errors. All components
reference Commons; Host references all components. Builds and tests clean.

src/ScadaLink.ExternalSystemGateway/Class1.cs

@@ -0,0 +1,6 @@
+namespace ScadaLink.ExternalSystemGateway;
+
+public class Class1
+{
+
+}