World props: fields and farmyards

Model and bake the 124 sprites of group farm of the world-props order (assets/requests/world-props/farm.md, brief assets/requests/world-props.md) on their own branch. Done when every sprite of the list is in assets/manifest.d/world_farm.toml, baked and reviewed on a gallery sheet.

All 124 sprites are baked (scripts in tools/blender/models/world_farm/) and reviewed on gallery sheets; field pieces were also checked in random-variant mosaics for seams.