feat: splashkit docker image

splashkit.Dockerfile

@@ -0,0 +1,67 @@
+FROM debian:bookworm-slim
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+# https://github.com/jenkinsci/docker/issues/543#issuecomment-318356276
+RUN echo "Acquire::http::Pipeline-Depth 0;" > /etc/apt/apt.conf.d/99custom && \
+  echo "Acquire::http::No-Cache true;" >> /etc/apt/apt.conf.d/99custom && \
+  echo "Acquire::BrokenProxy    true;" >> /etc/apt/apt.conf.d/99custom
+
+RUN rm -rf /var/lib/apt/lists/*
+RUN apt-get clean
+RUN apt-get update -o Acquire::CompressionTypes::Order::=gz
+
+RUN apt-get update && \
+  apt-get install -y --no-install-recommends --fix-missing \
+  curl \
+  git \
+  python3 \
+  python3-pip \
+  cmake \
+  pkg-config \
+  libpng16-16 \
+  libcurl4 \
+  libsdl2-2.0-0 \
+  libsdl2-mixer-2.0-0 \
+  libsdl2-gfx-1.0-0 \
+  libsdl2-image-2.0-0 \
+  libsdl2-net-2.0-0 \
+  libsdl2-ttf-2.0-0 \
+  build-essential \
+  fonts-dejavu-core \
+  clang \
+  ca-certificates \
+  sudo \
+  && rm -rf /var/lib/apt/lists/*
+
+# Install .NET
+RUN curl -L https://packages.microsoft.com/config/debian/12/packages-microsoft-prod.deb -o packages-microsoft-prod.deb && \
+  dpkg -i packages-microsoft-prod.deb && \
+  rm packages-microsoft-prod.deb
+
+RUN apt-get update && \
+  apt-get install -y --no-install-recommends \
+  dotnet-sdk-10.0 && \
+  apt-get clean && rm -rf /var/lib/apt/lists/*
+
+# Install SplashKit
+RUN curl -s https://raw.githubusercontent.com/splashkit/skm/master/install-scripts/skm-install.sh | bash
+ENV PATH="/root/.splashkit:${PATH}"
+RUN skm linux install
+
+# Pre-cache the SplashKit nuget package
+RUN mkdir -p /nuget-local
+RUN dotnet new console -n tmp && \
+  cd tmp && \
+  dotnet add package SplashKit --package-directory /nuget-local && \
+  cd .. && \
+  rm -rf tmp
+RUN dotnet nuget add source /nuget-local -n splashkit-local
+
+ENV DOTNET_RESTORE_SOURCES="/nuget-local"
+
+# Suppress audio/display warnings for headless SplashKit
+RUN echo "pcm.!default { type hw card 0 }" > /etc/asound.conf
+ENV SDL_AUDIODRIVER=dummy
+ENV XDG_RUNTIME_DIR=/tmp/runtime-root
+RUN mkdir -p $XDG_RUNTIME_DIR