Argon Atlas v54.0 — 275 models

Gemini 4 Argon released v54.0: 275 real-world 3D PBR models — 29.83M vertices, 56.92M triangles, 3,578/3,578 checks (commit 2bfe88c). New scenes: Whiteside Mountain NC, Grayson Highlands VA, Stone Mountain NC, Downtown Albany 3D, Redwood Filing-to-Lobby Wing. Includes KHR_mesh_quantization 16-bit POSITION encoding path from v50+.

Cadence: v51 260 → v52 265 → v53 270 → v54 275.