World props: shrines, magic and dungeon entrances

Model and bake the 114 sprites of group arcane of the world-props order (assets/requests/world-props/arcane.md, brief assets/requests/world-props.md) on their own branch. Done when every sprite of the list is in assets/manifest.d/world_arcane.toml, baked and reviewed on a gallery sheet.

All 114 sprites are modelled, baked and reviewed on gallery sheets (scripts in tools/blender/models/world_arcane/). For the dressing code: fairy_ring_piece variant v is the quarter of a ring centred on its tile's SE / SW / NW / NE corner (v = 0..3), so the four tiles around a corner close one ring.