Add MicCheck.Api.Tests.Integration project

NUnit integration tests that target a running API by URL and seed/clean
data directly in Postgres. Settings (BaseUrl, DbConnectionString) come
from .runsettings or environment variables so tests can be pointed at
any environment. HTTP requests live in HttpFiles/*.http; assertion
failures include a fresh DB snapshot of the relevant rows. First test
covers the flag-enabled path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/api/MicCheck.Api.Tests.Integration/MicCheck.Api.Tests.Integration.csproj

@@ -0,0 +1,28 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <LangVersion>latest</LangVersion>
+    <IsPackable>false</IsPackable>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
+    <PackageReference Include="Npgsql" Version="10.0.1" />
+    <PackageReference Include="NUnit" Version="4.5.1" />
+    <PackageReference Include="NUnit3TestAdapter" Version="6.2.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="HttpFiles\**\*.http">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+    <None Update="local.runsettings">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+</Project>