feat(site): modern dark SPA — all fluent CLI features in browser UI

- Rebuild site/index.html as full dark glass-morphism SPA (1295 lines)
  replacing the static README-copy with an interactive product experience
- Score tab: cosine-similarity engine in JS, task description + delegation
  intent inputs, top-3 cycle matches with animated per-dimension score bars
- Browse tab: live search + domain filter chips, responsive card grid with
  tags, summaries, and View YAML links
- Compare tab: partial 4D inputs (Delegation + Description), similarity
  matching, unique-cycle detection banner + Register flow when match < 40%
- Contribute tab: 3-step form, score-hint sliders with live sum validation,
  real-time YAML preview panel, pre-filled GitHub issue URL builder
- Hero: gradient headline, animated 4D dimension cards with per-D accent
  colors (purple/cyan/amber/emerald), stats strip, scroll CTA
- generate-knowledge-index.js: include full dimensions objects and
  score_hints in index.json (was only storing dimension key names and a
  200-char summary) — enables real client-side cosine scoring in browser
- Regenerate knowledge/index.json with full dimension text for all 16 entries

Author: faical-yannick-congo