FixMyEPUB missing-cover reference fixture

To the extent possible under law, the creator has waived all copyright and
related or neighboring rights to the EPUB fixture, its text, and its artwork
under CC0 1.0 Universal.

License: https://creativecommons.org/publicdomain/zero/1.0/

The fixture is provided without warranty. It is deliberately constructed for
testing: its EPUB 3 package contains cover artwork but omits the cover-image
property so that tools can reproduce and diagnose missing-cover behavior.