Replace the atlas_body_heightmaps DB-BLOB loader with a per-body file loader (D-202 amendment): heightmap.rs reads the 16-bit grayscale heightmap.png (via the new png dep) from the body's terrain_reference path, normalizes to f32 [0,1], and rejects RGB so a reliefmap can't be misread as elevation. Adds BodyHeightmap::downsample (box-average, deterministic) so Layer 1 drops the high-res stored heightmap to the 512x256 working resolution. sea_level becomes body metadata carried alongside, not in the PNG. 4 loader tests pass. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>