chore: bump NuGet packages (combined Dependabot updates) (#38)

- System.IO.Abstractions + TestingHelpers: 21.1.3 → 22.1.1
- Microsoft.Extensions.Logging.Abstractions: 9.0.4 → 10.0.5
- Microsoft.AspNetCore.Mvc.Testing: 10.0.0 → 10.0.5
- Microsoft.NET.Test.Sdk: 17.13.0 → 18.4.0

Closes #32, #33, #34, #35, #36

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mstroppel

src/backend/Directory.Packages.props

@@ -4,14 +4,14 @@
   </PropertyGroup>
   <ItemGroup>
     <!-- Core -->
-    <PackageVersion Include="System.IO.Abstractions" Version="21.1.3" />
-    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="9.0.4" />
+    <PackageVersion Include="System.IO.Abstractions" Version="22.1.1" />
+    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.5" />
     <!-- Tests -->
     <PackageVersion Include="FluentAssertions" Version="8.9.0" />
-    <PackageVersion Include="System.IO.Abstractions.TestingHelpers" Version="21.1.3" />
+    <PackageVersion Include="System.IO.Abstractions.TestingHelpers" Version="22.1.1" />
     <PackageVersion Include="xunit" Version="2.9.3" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="2.8.2" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
-    <PackageVersion Include="Microsoft.AspNetCore.Mvc.Testing" Version="10.0.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
+    <PackageVersion Include="Microsoft.AspNetCore.Mvc.Testing" Version="10.0.5" />
   </ItemGroup>
 </Project>