fix: replace sidebar label backdrop with theme-aware text shadow

src/App.vue

@@ -386,18 +386,6 @@ const menuOptions = computed<MenuOption[]>(() => {
         z-index: 30;
         overflow: visible;
     }
-    /* 浮层使用当前主题底色，保证文字不会与正文混在一起。 */
-    .admin-sider.is-collapsed::before {
-        content: '';
-        position: absolute;
-        inset: 0 auto 0 var(--admin-sider-collapsed);
-        width: calc(var(--admin-nav-reveal-width) - var(--admin-sider-collapsed));
-        background: var(--app-surface);
-        border-right: 1px solid var(--app-border);
-        opacity: 0;
-        pointer-events: none;
-        transition: opacity 0.2s ease;
-    }
     .admin-sider.is-collapsed .admin-nav-scroll.n-scrollbar,
     .admin-sider.is-collapsed .admin-sider-footer {
         position: relative;
@@ -407,9 +395,6 @@ const menuOptions = computed<MenuOption[]>(() => {
         clip-path: inset(0 calc(var(--admin-nav-reveal-width) - var(--admin-sider-collapsed)) 0 0);
         transition: clip-path 0s 0.2s;
     }
-    .admin-sider.is-collapsed:is(:hover, :has(:focus-visible))::before {
-        opacity: 1;
-    }
     .admin-sider.is-collapsed:is(:hover, :has(:focus-visible)) .admin-nav-scroll.n-scrollbar,
     .admin-sider.is-collapsed:is(:hover, :has(:focus-visible)) .admin-sider-footer {
         clip-path: inset(0);
@@ -423,6 +408,10 @@ const menuOptions = computed<MenuOption[]>(() => {
     }
     .admin-sider.is-collapsed .admin-menu-label,
     .admin-sider.is-collapsed .admin-settings-label {
+        /* 仅为字形添加随主题变化的柔和阴影，不绘制背景或边框。 */
+        text-shadow:
+            0 0 3px var(--app-surface),
+            0 1px 6px var(--app-surface);
         transform: translateX(-6px);
     }
     .admin-sider.is-collapsed:is(:hover, :has(:focus-visible)) .n-menu-item-content-header,
@@ -488,7 +477,6 @@ const menuOptions = computed<MenuOption[]>(() => {
 @media (prefers-reduced-motion: reduce) {
     .admin-sider,
     .admin-sider.is-collapsed,
-    .admin-sider.is-collapsed::before,
     .admin-sider.is-collapsed .admin-nav-scroll.n-scrollbar,
     .admin-sider.is-collapsed .admin-sider-footer,
     .admin-sider .n-menu-item-content-header,