💄 style(layout): 优化侧边栏样式和布局

- 移除桌面端侧边栏多余的flex flex-col类
- 简化移动端侧边栏容器结构，移除不必要的flex-1 overflow-hidden包装
- 统一侧边栏样式代码，提高可维护性

web/src/client/admin/layouts/MainLayout.tsx

@@ -196,7 +196,7 @@ export const MainLayout = () => {
     <div className="flex h-screen bg-background">
       {/* Desktop Sidebar */}
       <aside className={cn(
-        "hidden md:block border-r bg-background transition-all duration-200 flex flex-col",
+        "hidden md:block border-r bg-background transition-all duration-200",
         collapsed ? "w-16" : "w-64"
       )}>
         <DesktopSidebarContent />
@@ -204,13 +204,11 @@ export const MainLayout = () => {
 
       {/* Mobile Sidebar */}
       <Sheet open={isMobileMenuOpen} onOpenChange={setIsMobileMenuOpen}>
-        <SheetContent side="left" className="w-64 p-0 flex flex-col h-full">
+        <SheetContent side="left" className="w-64 p-0">
           <SheetHeader className="p-4 border-b">
             <SheetTitle>{appName}</SheetTitle>
           </SheetHeader>
-          <div className="flex-1 overflow-hidden">
-            <MobileSidebarContent />
-          </div>
+          <MobileSidebarContent />
         </SheetContent>
       </Sheet>