Living Villages 1.7.0-preview.21

Targeted autonomous-site fix:
- preserves Preview.20 chunk-loading and mountain-slope tolerance
- treats solid subsurface geology as valid even when it is ore or modded rock
- still rejects underground air/soft cavities
- still rejects block entities, TerrainProtection, MineColonies protected buildings, and unsafe surface/above-surface blocks

Reason: the old 21x21 safety scan extended up to 12 blocks below the surface and rejected any block not in the narrow ground whitelist. A single ore vein could invalidate an otherwise safe building site before MineColonies template selection was ever reached.
