feat(notifications): add notification sound playback for new alerts and include sound file documentation

src/contexts/NotificationContext.jsx

@@ -3,6 +3,24 @@ import toast from 'react-hot-toast';
 import { useAuth } from './AuthContext';
 import api from '../services/api';
 
+// Lazily created Audio instance — reused across calls to avoid memory churn
+let _audio = null;
+function playNotificationSound() {
+  try {
+    if (!_audio) {
+      _audio = new Audio('/sounds/notification.mp3');
+      _audio.volume = 0.5;
+    }
+    // Reset to start so rapid arrivals always play from beginning
+    _audio.currentTime = 0;
+    _audio.play().catch(() => {
+      // Autoplay blocked (user hasn't interacted yet) or file missing — silent fail
+    });
+  } catch {
+    // Ignore any other errors (e.g. unsupported format)
+  }
+}
+
 const NotificationContext = createContext();
 
 export function NotificationProvider({ children }) {
@@ -30,6 +48,9 @@ export function NotificationProvider({ children }) {
 
       // Subsequent fetches: toast new unread notifications
       const newItems = incoming.filter(n => !n.read && !seenIds.current.has(n.id));
+      if (newItems.length > 0) {
+        playNotificationSound();
+      }
       newItems.forEach(n => {
         seenIds.current.add(n.id);
         const icon = notificationIcon(n.type);