Phase 0 WP-0.10–0.12: Host skeleton, options classes, sample configs, and execution framework

- WP-0.10: Role-based Host startup (Central=WebApplication, Site=generic Host),
  15 component AddXxx() extension methods, MapCentralUI/MapInboundAPI stubs
- WP-0.11: 12 per-component options classes with config binding
- WP-0.12: Sample appsettings for central and site topologies
- Add execution procedure and checklist template to generate_plans.md
- Add phase-0-checklist.md for execution tracking
- Resolve all 21 open questions from plan generation
- Update IDataConnection with batch ops and IAsyncDisposable
57 tests pass, zero warnings.

src/ScadaLink.ExternalSystemGateway/ScadaLink.ExternalSystemGateway.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>net10.0</TargetFramework>
@@ -7,6 +7,11 @@
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="10.0.5" />
+    <PackageReference Include="Microsoft.Extensions.Options" Version="10.0.5" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="../ScadaLink.Commons/ScadaLink.Commons.csproj" />
   </ItemGroup>