Apple's developer.apple.com ships a classic BMP/DIB favicon.ico rather
than a PNG one, so the icon discovery that feeds the ZIM book icon found
nothing and the archive shipped without an Illustrator_48x48@1 image.
Decode the .ico container directly: read the directory, pick the largest
entry, and decode it either as the PNG a modern favicon embeds or as the
BITMAPINFOHEADER bitmap older ones still carry. The BMP path handles
32/24/8/4/1 bpp, the stacked AND transparency mask, and the all-zero
alpha case where a 32-bpp icon leans on the mask for its shape.
A pure-Go .icns writer (PNG-embedded entries from 16 to 1024) and a finder that
digs the site's favicon out of a cloned mirror, preferring a large apple-touch
icon and unwrapping a PNG-based .ico. These feed the bundle icon for the upcoming
app formats. Adds golang.org/x/image for high-quality resampling.
Tam Nguyen Duc