feat: dreport-service + dreport-ffi + nuget packages

Extract orchestration (font registry + render pipeline) from the Axum
backend into a standalone dreport-service crate. Backend becomes a thin
HTTP adapter on top.

Add dreport-ffi (cdylib) exposing the service through a stable C ABI
with opaque handles, byte buffers, and thread-local error reporting.

Build Dreport.Service + Dreport.AspNetCore NuGet packages under
bindings/dotnet/, packing the host RID native binary via a generated
nuspec. justfile recipes (nuget-publish, nuget-publish-all) build,
pack, and push to the Gitea NuGet registry in one shot.

Test coverage: 47 Rust + 38 C# (xUnit + WebApplicationFactory).

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

bindings/dotnet/tests/Dreport.Service.Tests/Dreport.Service.Tests.csproj

@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <IsPackable>false</IsPackable>
+    <LangVersion>latest</LangVersion>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <!-- Tests run on the host RID; ensure native dylibs ship next to the test asm. -->
+    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+    <PackageReference Include="xunit" Version="2.9.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Dreport.Service\Dreport.Service.csproj" />
+  </ItemGroup>
+
+  <!-- Sample TTF for FontParseException tests; copied from the workspace assets dir. -->
+  <ItemGroup>
+    <None Include="..\..\..\..\dreport-service\assets\fonts\NotoSans-Regular.ttf"
+          Link="fixtures/NotoSans-Regular.ttf"
+          CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
+</Project>