Add missing Steam UI runtime libraries.

Install libXtst and related 64/32-bit dependencies required for steamui/webhelper startup inside containers.

Co-authored-by: Cursor <cursoragent@cursor.com>

Dockerfile

@@ -23,6 +23,10 @@ RUN wget "https://github.com/LizardByte/Sunshine/releases/download/v0.21.0/sunsh
 RUN apt-get update && \
     echo "debconf steam/question select I AGREE" | debconf-set-selections \
     && apt-get install -y /tmp/sunshine.deb steam:i386 steam-devices \
+    libxtst6 libxtst6:i386 \
+    libxss1 libxss1:i386 \
+    libnss3 libnss3:i386 \
+    libxi6 libxi6:i386 \
     && locale-gen en_US.UTF-8 \
     && rm -f /tmp/sunshine.deb \
     && apt-get clean \