fix(docker): add unzip to image (required by GLM dep build)

A clean dependency build failed immediately at the GLM step with
`unzip: command not found`. build-glm.sh extracts glm-0.9.9.8.zip with unzip,
but the Ubuntu-based image (introduced when the emsdk image was replaced) never
installed it. Add unzip to the apt-get list.

Verified: GLM, zstd and protobuf now build and stamp, and the deps build
proceeds into boost.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docker/Dockerfile

@@ -22,6 +22,7 @@ RUN apt-get update && apt-get install -y \
     ccache \
     rsync \
     xz-utils \
+    unzip \
     && rm -rf /var/lib/apt/lists/*
 
 # Install emsdk from source (same approach as scripts/setup-emsdk.sh)