Phase 1 D: expedition ground receded (project-owned dark sand material)

'sand 1' shipped pure-white BaseColor - the whole desert washed out and
characters/telegraphs sat on a bright field. Project-owned copy
(Mat_Ground_Arid_Dark, 0.72/0.68/0.63) assigned to both room-slot grounds;
the Synty pack asset stays pristine. Clarity doctrine: ground darker +
lower-detail than characters.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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