Third-party artwork and icon attribution

Selected interface icons are adapted from Game-icons.net artwork by Lorc,
Delapouite, Skoll, sbed, and Cathelineau. Licensed under Creative Commons
Attribution 3.0: https://creativecommons.org/licenses/by/3.0/
Source: https://game-icons.net/

The homepage uses these public-domain artworks from Wikimedia Commons:
- Sitting Alone by a Stream, attributed to Fan Kuan:
  https://commons.wikimedia.org/wiki/File:Fan_Kuan-Sitting_Alone_by_a_Stream.jpg
- Dwelling in the Fuchun Mountains, attributed to Huang Gongwang:
  https://commons.wikimedia.org/wiki/File:Dwelling_in_the_Fuchun_Mountains_(second_half).jpg

Bundled React, React DOM, and Babel license notices are in /vendor/.