feat: add notification bell with persistent download log

- Bell icon in sidebar and mobile header with unread badge
- On download complete/error: saves notification to localStorage (survives reload)
- Playlist/album downloads: parses job log to list which tracks failed
- Panel toggles open with animation, click-outside closes it
- Each notification dismissable with X; "clear all" button
- Notifications capped at 100 entries in localStorage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main.js

@@ -29,6 +29,7 @@ import {
   selectDlType, executeDownload, executeSpotifyDownload, openEditPlModal, closeEditPlModal,
   saveEditPlaylist, editPlUploadCover, editPlCoverSelected, editPlRemoveCover,
   toggleMobileSearch, closeMobileSearch, switchSetupTab,
+  toggleNotifPanel, deleteNotif, clearNotifs, initNotifBell,
 } from './ui.js';
 
 // ─── CONNECT ───
@@ -80,6 +81,7 @@ async function startApp() {
     navigate('home');
   }
   loadHomeData();
+  initNotifBell();
   _restoreLastPlayed();
   if(localStorage.getItem('ns_radio')==='1') { S.radioMode=true; _applyRadioBtn(); }
 }
@@ -235,6 +237,7 @@ Object.assign(window, {
   openEditPlModal, closeEditPlModal, saveEditPlaylist,
   editPlUploadCover, editPlCoverSelected, editPlRemoveCover,
   toggleMobileSearch, closeMobileSearch, switchSetupTab,
+  toggleNotifPanel, deleteNotif, clearNotifs,
   // App
   doConnect, disconnect,
 });