test(acl): OpenZaak default-fills ZGW fields and posts to OpenZaak (refs #5)

Add the ACL skeleton (Application/Infrastructure/Api per §9) and failing
xUnit tests for the single operation: AclService.OpenZaakAsync must
default-fill bronorganisatie, verantwoordelijkeOrganisatie, startdatum
(clock) and vertrouwelijkheidaanduiding and delegate to the gateway; the
OpenZaakGateway must POST the zaak to OpenZaak with a Bearer JWT and the
default-filled body. Implementations throw NotImplementedException — red.

Also add ADR-0003 (default-fill strategy).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/acl/Acl.Tests/Acl.Tests.csproj

@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Acl.Application\Acl.Application.csproj" />
+    <ProjectReference Include="..\Acl.Infrastructure\Acl.Infrastructure.csproj" />
+  </ItemGroup>
+
+</Project>