WebSocket /ws/collab/{vault}/{path} (rooms par fichier), relais Yjs/CRDT, awareness (curseurs colores + presence), persistance serveur debounce 2s, auth WS + check_vault_access, reconnexion automatique. Frontend frontend/js/collab.js, backend backend/collab.py. Tests: 17 backend (5 clients simultanes) + 10 frontend. Docs: CHANGELOG, ROADMAP, fiche features/collaboration.md, README FR/EN.
