FEATURE: Add libavif-bin for AVIF image optimization

[gradinarufelix]

Adds libavif-bin to build_image_optimizers() in root-files/build.sh, alongside the existing jpegoptim / pngquant / webp / etc. tooling.

libavif-bin provides the avifenc and avifdec CLIs, needed for AVIF post-processing — e.g. by Sitegeist.Iconoclasm on Neos sites that now serve AVIF sources.

The package pulls in only libavif + libyuv0.

Test

Built the patched image locally against harbor.flownative.io/docker/php:8.4 and inspected the resulting container:

docker build --build-arg PHP_BASE_IMAGE=harbor.flownative.io/docker/php:8.4 -t beach-php-libavif-test .
docker run --rm --entrypoint sh beach-php-libavif-test -c \
  'which avifenc avifdec cwebp jpegoptim pngquant && avifenc --version | head -1'

Result:

/usr/bin/avifenc
/usr/bin/avifdec
/usr/bin/cwebp
/usr/bin/jpegoptim
/usr/bin/pngquant
Version: 0.11.1 (dav1d [dec]:1.0.0, libgav1 [dec]:0.18.0, aom [enc/dec]:v3.6.0, rav1e [enc]:0.5.1 (v0.5.1), svt [enc]:v1.4.1)

• New: avifenc / avifdec available (libavif 0.11.1 from Debian 12 bookworm).
• No regression: existing optimizers (cwebp, jpegoptim, pngquant) still present.
• Build completed cleanly with no new warnings beyond the pre-existing InvalidDefaultArgInFrom notice.