docs(site): landing v2 — spec-sheet design + core narrative sections

Full landing redesign in an engineering spec-sheet aesthetic (blueprint
grid, mono kickers, Bricolage Grotesque display, gradient second beat):

- hero artifact card tells the whole loop in one visual: requirement →
  Claude Code writes typed metadata (diff) → os validate ✓ → os dev preview
- 01 The loop: create-objectstack → describe (agent writes, gate rejects)
  → preview in browser; requirement changes run the same loop
- 02 The gates: typed / validated / reviewed / governed
- 03 The vocabulary: 12 metadata capabilities for enterprise software +
  the one-off-codebase contrast + stats strip (1,600+ schemas, 5 drivers,
  7 adapters, MCP)

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

Author: os-zhuang