Refactor: Rename DocumentOperator to DocumentService

Renamed and restructured project references across the solution
to replace `DocumentOperator` projects with `DocumentService`
projects. Updated all `.csproj` files to reflect the new project
names and references.

Modified the solution file (`DocumentOperator.sln`) to remove
`DocumentOperator` projects and add corresponding `DocumentService`
projects, including `DocumentService.API`, `DocumentService.Application`,
`DocumentService.Infrastructure`, `DocumentService.Domain`, and
`DocumentService.Tests`.

This change aligns the project structure with the new naming
convention or organizational standards.

DocumentOperator.Tests/DocumentService.Tests.csproj

@@ -0,0 +1,48 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <None Remove="TestData\Pdfs\pdfWithSwissQRCode.pdf" />
+    <None Remove="TestData\Pdfs\valid.pdf" />
+    <None Remove="TestData\Pdfs\pdfWithMoreThanOneAttachment.pdf" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <EmbeddedResource Include="TestData\Pdfs\pdfWithSwissQRCode.pdf" />
+    <EmbeddedResource Include="TestData\Pdfs\valid.pdf" />
+    <EmbeddedResource Include="TestData\Pdfs\pdfWithMoreThanOneAttachment.pdf" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.0" />
+    <PackageReference Include="FluentAssertions" Version="7.0.0" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="8.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="Moq" Version="4.20.72" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\DocumentOperator.API\DocumentService.API.csproj" />
+    <ProjectReference Include="..\DocumentOperator.Domain\DocumentService.Domain.csproj" />
+    <ProjectReference Include="..\DocumentOperator.Application\DocumentService.Application.csproj" />
+    <ProjectReference Include="..\DocumentOperator.Infrastructure\DocumentService.Infrastructure.csproj" />
+  </ItemGroup>
+
+</Project>