fix: aumentar z-index del header y dropdown

- Agregar z-index: 100 al app-header
- Aumentar z-index del dropdown a 10001 (mayor que AuthIndicator)
- Asegurar que el dropdown se dibuje por encima de todos los elementos

components/MainContainer.client.vue

@@ -96,6 +96,7 @@ const hasActiveTrack = computed(() => !!props.currentTrack)
   position: relative;
   overflow: visible;
   flex-shrink: 0;
+  z-index: 100;
 }
 
 .app-header::before {

components/SettingsMenu.client.vue

@@ -94,7 +94,7 @@ onUnmounted(() => {
   border-radius: 16px;
   padding: 12px;
   box-shadow: var(--shadow-glass), 0 8px 32px rgba(0, 0, 0, 0.2);
-  z-index: 9999;
+  z-index: 10001;
   display: flex;
   flex-direction: column;
   gap: 8px;