feat: collaboration temps reel - edition simultanee (#62)

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.

frontend/locales/en.json

@@ -306,6 +306,11 @@
   "common.search": "Search",
   "common.unknown": "Unknown",
   "common.yes": "Yes",
+  "collab.peers_title": "{count} person(s) connected",
+  "collab.presence_title": "Real-time collaboration",
+  "collab.status_connected": "Collaboration active",
+  "collab.status_connecting": "Connecting to collaboration…",
+  "collab.status_disconnected": "Collaboration lost — reconnecting…",
   "config.about": "About",
   "config.about_error": "Loading error",
   "config.about_loading": "Loading...",

frontend/locales/fr.json

@@ -306,6 +306,11 @@
   "common.search": "Rechercher",
   "common.unknown": "Inconnue",
   "common.yes": "Oui",
+  "collab.peers_title": "{count} personne(s) connectée(s)",
+  "collab.presence_title": "Collaboration temps réel",
+  "collab.status_connected": "Collaboration active",
+  "collab.status_connecting": "Connexion à la collaboration…",
+  "collab.status_disconnected": "Collaboration interrompue — reconnexion…",
   "config.about": "À propos",
   "config.about_error": "Erreur de chargement",
   "config.about_loading": "Chargement...",