fix: resolve notification routing bug, audio playback format, and backend 500 errors

- Fixed audio playback by downloading a valid mp3 file and importing it directly via Vite.

- Fixed the route collision where DELETE /notifications/clear-all was being captured by /notifications/:id.

- The notification badge now automatically clears (optimistic UI update) when the tray is opened.

- The backend no longer throws a 500 error when querying users during impersonation handoffs.

backend/index.js

@@ -515,18 +515,6 @@ apiRouter.get('/notifications', async (req, res) => {
   }
 });
 
-apiRouter.put('/notifications/:id', async (req, res) => {
-  try {
-    await pool.query(
-      'UPDATE notifications SET is_read = true WHERE id = ? AND user_id = ?',
-      [req.params.id, req.user.id]
-    );
-    res.json({ message: 'Notification marked as read' });
-  } catch (error) {
-    res.status(500).json({ error: error.message });
-  }
-});
-
 apiRouter.put('/notifications/read-all', async (req, res) => {
   try {
     await pool.query(
@@ -539,13 +527,13 @@ apiRouter.put('/notifications/read-all', async (req, res) => {
   }
 });
 
-apiRouter.delete('/notifications/:id', async (req, res) => {
+apiRouter.put('/notifications/:id', async (req, res) => {
   try {
     await pool.query(
-      'DELETE FROM notifications WHERE id = ? AND user_id = ?',
+      'UPDATE notifications SET is_read = true WHERE id = ? AND user_id = ?',
       [req.params.id, req.user.id]
     );
-    res.json({ message: 'Notification deleted' });
+    res.json({ message: 'Notification marked as read' });
   } catch (error) {
     res.status(500).json({ error: error.message });
   }
@@ -563,6 +551,18 @@ apiRouter.delete('/notifications/clear-all', async (req, res) => {
   }
 });
 
+apiRouter.delete('/notifications/:id', async (req, res) => {
+  try {
+    await pool.query(
+      'DELETE FROM notifications WHERE id = ? AND user_id = ?',
+      [req.params.id, req.user.id]
+    );
+    res.json({ message: 'Notification deleted' });
+  } catch (error) {
+    res.status(500).json({ error: error.message });
+  }
+});
+
 // --- Funnel Routes ---
 apiRouter.get('/funnels', async (req, res) => {
   try {