Replaces the legacy color-only *.tilemap.json fixtures with baked
2-tile atlas-sets in the new atlases/<id>/{diffuse,height,atlas-json,
lock-json} layout. Stub PNGs are 32x32 solid colors matching the
previous color values; height channel is synthesized L8=0 by the baker.
A scripts/bake.sh re-bake helper drives the atlas-baker tool against
assets/_sources/.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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