优化 NavbarThemeSwitcher 组件，更新主题图标为水平渐变，以提升视觉一致性。同时，调整 ShortcutBar 组件中的图标颜色为主色，增强用户体验。

src/layouts/components/NavbarThemeSwitcher.vue

@@ -25,7 +25,7 @@ const themes: ThemeSwitcherTheme[] = [
   {
     name: 'transparent',
     title: '透明',
-    icon: 'mdi-gradient-vertical',
+    icon: 'mdi-gradient-horizontal',
   },
 ]
 </script>

src/layouts/components/ShortcutBar.vue

@@ -178,7 +178,7 @@ onMounted(() => {
               @click="openDialog(item.dialogRef)"
             >
               <VAvatar variant="tonal" size="48" class="me-4" rounded="lg">
-                <VIcon :icon="item.icon" size="24" />
+                <VIcon color="primary" :icon="item.icon" size="24" />
               </VAvatar>
               <div>
                 <div class="text-body-1 text-high-emphasis font-weight-medium">{{ item.title }}</div>