feat(notifications): wire client Socket.IO to /notifications namespace with toast + E2E

- Connect to /notifications namespace (matches backend NotificationsGateway)
- Pass JWT token in Socket.IO auth handshake for proper authentication
- Listen for server-pushed notification:unread-count to sync badge
- Show sonner toast on notification:new events
- Add setUnreadCount action to notifications store
- Add E2E round-trip tests (auth connect, reject invalid, multi-device)
- Fix inquiry handler test: event name inquiry.created → inquiry.received

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/inquiries/application/__tests__/create-inquiry.handler.spec.ts

@@ -94,7 +94,7 @@ describe('CreateInquiryHandler', () => {
     expect(mockEventBus.publish).toHaveBeenCalledTimes(1);
     expect(mockEventBus.publish).toHaveBeenCalledWith(
       expect.objectContaining({
-        eventName: 'inquiry.created',
+        eventName: 'inquiry.received',
         listingId: 'listing-1',
         userId: 'user-1',
       }),