An SVG starting with an XML comment holding "ftypavis" passes the
first-bytes check for AVIF; resized as PNG, it is answered 200 with the
SVG rendered. The new server test asks for it through both image routes,
resized and as orig, and wants 415 for each. The new processor test
checks that an image in each of the six source formats loads and is saved
again in its own format.
Model: opus-5-5
