Full redesign of the standalone invite page for the 2026 edition (20-23 August,
Labenne-Ocean, jour J samedi 22). Concept: intrication (entanglement) - two
states, one system, communicating across distance. Dark OKLCH design system with
a paired cyan/magenta accent language, an EntanglementField canvas (starfield +
mirrored particle pairs + 67Hz interference waveform), Archivo (wdth) + Martian
Mono, replacing the v0 light theme.

- new EntanglementField signature canvas (DPR-capped, mobile-scaled, full
  prefers-reduced-motion static path)
- sections: hero, concept, jour-J lineup, sejour, hebergement, transport,
  packing, v0 souvenirs (lifted audio embeds + accessible photo lightbox), RSVP
- countdown retargeted to 2026-08-22, hydration-safe placeholder
- lightbox renders full-size via plain img with managed focus
- add PRODUCT.md / DESIGN.md design context at repo root

Verified: clean SSG build (6.3 kB), WCAG AA contrast, zero console errors,
correct SSR + reduced-motion paths.