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

README.md

@@ -37,6 +37,8 @@ Image: `git.eeqj.de/sneak/baseimage`, built for `linux/amd64` and
 | tzdata          | apt                            | `/usr/share/zoneinfo`          |
 | zstd            | apt                            | `/usr/bin/zstd`                |
 | sqlite3 (CLI)   | apt                            | `/usr/bin/sqlite3`             |
+| libvips         | apt `libvips-dev`, `libvips-tools` | `vips` on `PATH`          |
+| libheif         | apt `libheif-dev`, `libheif-plugin-aomenc` | HEIF/AVIF codec   |
 
 Plus the usual odds and ends: `git`, `curl`, `wget`, `jq`, `rsync`,
 `openssh-client`, `zip`/`unzip`, `xz-utils`, `bzip2`, and the `-dev`

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"

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