World props: bones, graves and battlefields

Model and bake the 115 sprites of group remains of the world-props order (assets/requests/world-props/remains.md, brief assets/requests/world-props.md) on their own branch. Done when every sprite of the list is in assets/manifest.d/world_remains.toml, baked and reviewed on a gallery sheet.

All 115 baked on branch claude/props-remains-205ac8 (scripts tools/blender/models/world_remains/, manifest assets/manifest.d/world_remains.toml) and reviewed on gallery sheets. Open point for the bake: grave_mound_old is ordered with 4 facings x 2 variants, which the baker cannot combine; its two variants are the two orientations.