feat: add navigation button to notifications for direct song/album/playlist access

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

styles.css

@@ -104,6 +104,8 @@ nav{flex:1;overflow-y:auto;padding:4px 10px}
 .notif-x{background:none;border:none;cursor:pointer;color:var(--text3);font-size:13px;padding:0;line-height:1;flex-shrink:0;transition:color .15s}
 .notif-x:hover{color:var(--text)}
 .notif-msg{font-size:12px;color:var(--text2);margin-top:6px}
+.notif-nav-btn{margin-top:8px;background:none;border:1px solid var(--accent-dim);border-radius:6px;color:var(--accent);font-size:12px;padding:4px 10px;cursor:pointer;transition:background .15s,color .15s}
+.notif-nav-btn:hover{background:var(--accent);color:#fff}
 .notif-failed{margin-top:6px}
 .notif-failed summary{font-size:11px;color:var(--accent);cursor:pointer;user-select:none}
 .notif-failed ul{margin:4px 0 0 14px;padding:0;font-size:11px;color:var(--text3)}