Add mouse-wheel volume control in popup

popup.js

@@ -162,4 +162,15 @@ document.addEventListener("keydown", (e) => {
   if (e.key === "ArrowDown") { e.preventDefault(); setVolume(v - stepDownFrom(v)); }
 });
 
+// Mausrad im Popup: Lautstärke ändern (adaptive Schritte).
+// Verhindert das Scrollen/Zoomen der Seite, solange das Popup offen ist.
+document.addEventListener("wheel", (e) => {
+  e.preventDefault();
+  const v = Number(slider.value);
+  const delta = e.deltaY < 0
+    ? stepUpFrom(v)
+    : -stepDownFrom(v);
+  setVolume(v + delta);
+}, { passive: false });
+
 init();