🔹 Ch.13 — Octahedron (Air) [Lane D] · refs #30

# Ch.13 — Octahedron

**Part**: III | **Lane**: D | **Refs**: #30 · #63

## Rule of Three
1. Core — octahedral dual of cube
2. Sacred — inscribed octahedron
3. Philosophy — Plato's Air
4. Empirical — molecular geometry
5. Image — octahedron

## Acceptance
- [ ] ≥8 pages | `Closes #77`