feat(site): overhaul UX, demos, and branding

[Obsecurus]

Summary

• redesign GitHub Pages site with a dark visual system and clearer stakeholder messaging
• add interactive scenario explorer (command/output/stats/insights tabs) backed by real captured scenario data
• add analyst loop visualization and a codex-guided LLM refinement demo with measured loop deltas
• refresh branding with a new logo, site mark, and favicon, and align README header links/content
• add site data provenance notes for reproducible demo artifacts

Validation

• node --check site/app.js
• cargo test --workspace