feat: add backend .NET project with Domain, Infrastructure, API, and CLI

src/ParagonPlayground/backend/Dockerfile

@@ -0,0 +1,27 @@
+FROM mcr.microsoft.com/dotnet/sdk:10.0 AS build
+WORKDIR /src
+
+COPY ParagonPlayground.slnx ./
+COPY Directory.Build.props ./
+COPY src/Directory.Build.props src/
+COPY src/Directory.Packages.props src/
+COPY src/ParagonPlayground.Domain/ParagonPlayground.Domain.csproj src/ParagonPlayground.Domain/
+COPY src/ParagonPlayground.Infrastructure/ParagonPlayground.Infrastructure.csproj src/ParagonPlayground.Infrastructure/
+COPY src/ParagonPlayground.Api/ParagonPlayground.Api.csproj src/ParagonPlayground.Api/
+RUN dotnet restore src/ParagonPlayground.Api/ParagonPlayground.Api.csproj
+
+COPY . .
+RUN dotnet publish src/ParagonPlayground.Api/ParagonPlayground.Api.csproj -c Debug -o /app
+
+FROM mcr.microsoft.com/dotnet/aspnet:10.0 AS runtime
+WORKDIR /app
+EXPOSE 8080
+COPY --from=build /app .
+
+RUN apt-get update && \
+    apt-get install -y unzip curl && \
+    curl -sSL https://aka.ms/getvsdbgsh | /bin/sh /dev/stdin -v latest -l /vsdbg && \
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/*
+
+ENTRYPOINT ["dotnet", "ParagonPlayground.Api.dll"]