Add a source-grounded 3D Model Atlas

[Doppp]

Summary

• add @explorables/model-atlas with strict inert descriptors/traces, evidence-aware comparison, semantic fallback, and bounded Three.js rendering
• add an exact tiny-Transformer trace, published GPT-1/2/3 views, GPT-4's explicit disclosure boundary, and source-gated DeepSeek V4, Kimi K3, Qwen 3, MiniMax M1, and GLM 5.2 views
• integrate the Atlas into AI from First Principles without a new Markdown directive or relaxed sandbox permission
• update the PRD, architecture, authoring guide, roadmap, security guidance, changelog, and implementation status

Verification

• pnpm check — 33 suites / 100 tests
• pnpm build
• pnpm test:browser — 15 tests
• pnpm site:test — 2 tests
• pnpm audit --audit-level high
• clean clone: Node 24.19.0 / pnpm 11.15.1 frozen install, check, build
• clean clone: Node 22.22.2 / pnpm 10.26.0 frozen install, check, build
• in-app browser inspection of the model selector, semantic trace, evidence boundary, and capstone layout

Source boundary

Frontier-family entries remain candidate mechanism views. They intentionally omit unfrozen counts and dimensions until the planned course-local source and licence freezes are complete.