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/sw.js

@@ -1,5 +1,5 @@
 /* ObsiGate — Service Worker (PWA offline + push)
- * Version: 2 (2026-09-11)
+ * Version: 3 (2026-09-11)
  *
  * Caching policy (fixes stale-asset loads behind Cloudflare / mobile):
  *   - navigations & code (HTML / JS / CSS / manifest) : NETWORK-FIRST
@@ -11,7 +11,7 @@
  * cache or Cloudflare does NOT clear the Service Worker Cache Storage, which is
  * a separate store. Bumping SW_VERSION invalidates it on every release.
  */
-const SW_VERSION = 'v2';
+const SW_VERSION = 'v3';
 const CODE_CACHE = `obsigate-code-${SW_VERSION}`;
 const RUNTIME_CACHE = `obsigate-runtime-${SW_VERSION}`;
 const API_CACHE = `obsigate-api-${SW_VERSION}`;
@@ -38,6 +38,7 @@ const PRECACHE_URLS = [
   '/static/js/offline-db.js',
   '/static/js/sync.js',
   '/static/js/legacy.js',
+  '/static/js/collab.js',
 ];
 
 // ── Install: precache the shell, then activate immediately ──────────────────