feat: implement NotificationsHub for real-time vault sync notifications

- Added NotificationsHub durable object to handle WebSocket connections for vault sync notifications.
- Integrated SignalR protocol for message framing and communication.
- Updated storage service methods to return revision date and user ID for vault sync notifications.
- Enhanced existing handlers (attachments, ciphers, folders, sends, and import) to notify users of vault sync events.
- Created new notifications handler for WebSocket negotiation and binding user IDs.
- Updated frontend to establish WebSocket connection for receiving vault sync notifications.
- Improved CORS headers to support new notification endpoints.
- Bumped wrangler version in package.json to 4.71.0.

src/types/index.ts

@@ -1,6 +1,7 @@
 // Environment bindings
 export interface Env {
   DB: D1Database;
+  NOTIFICATIONS_HUB: DurableObjectNamespace;
   // Prefer R2 when available. Optional to support KV-only deployments.
   ATTACHMENTS?: R2Bucket;
   // Optional fallback for attachment/send file storage (no credit card required).