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

bin/test

@@ -26,6 +26,8 @@ docker run --rm "$img" bash -ec '
     test -e /usr/share/zoneinfo/America/New_York
     zstd --version
     sqlite3 --version
+    vips --version
+    vips -l | grep -i heif > /dev/null
 '
 
 echo "== $img: runit service lifecycle"