Add libvips and libheif with development headers (closes #6)

Install libvips-dev, libvips-tools, libheif-dev and
libheif-plugin-aomenc from apt. libvips-tools provides the vips CLI,
which the smoke test uses to confirm libheif is linked as a loader.

Model: deepseek-v4-pro

build.sh

@@ -28,7 +28,8 @@ apt-get -y install --no-install-recommends \
     tk-dev uuid-dev zlib1g-dev \
     shellcheck \
     tzdata \
-    zstd sqlite3
+    zstd sqlite3 \
+    libvips-dev libvips-tools libheif-dev libheif-plugin-aomenc
 
 # --- Go (latest) -------------------------------------------------------------
 gover="$(curl -fsSL 'https://go.dev/VERSION?m=text' | head -n1)"
@@ -107,6 +108,8 @@ shellcheck --version
 test -e /usr/share/zoneinfo/America/New_York
 zstd --version
 sqlite3 --version
+vips --version
+vips -l | grep -i heif > /dev/null
 hugo version
 node --version
 npm --version