fix: corrige avisos de estilo do Tailwind CSS

- bg-gradient-to-r -> bg-linear-to-r
- after:start-[4px] -> after:start-1
- z-[60] -> z-60

frontend/src/components/Header.tsx

@@ -91,7 +91,7 @@ export default function Header() {
     <>
       {/* Admin Bar - aparece apenas para usuários logados */}
       {isLoggedIn && (
-        <div className="w-full bg-secondary dark:bg-black py-1.5 px-4 z-[60] relative">
+        <div className="w-full bg-secondary dark:bg-black py-1.5 px-4 z-60 relative">
           <div className="container mx-auto flex items-center justify-between">
             <div className="flex items-center gap-2 text-xs text-gray-400">
               <i className="ri-shield-user-line text-primary"></i>

frontend/src/components/admin/BackupManager.tsx

@@ -192,7 +192,7 @@ export function BackupManager() {
   return (
     <div className="space-y-6">
       {/* Botão de Criar Backup */}
-      <div className="bg-gradient-to-r from-blue-50 to-blue-100 dark:from-blue-900/20 dark:to-blue-800/20 border border-blue-200 dark:border-blue-800 rounded-2xl p-6">
+      <div className="bg-linear-to-r from-blue-50 to-blue-100 dark:from-blue-900/20 dark:to-blue-800/20 border border-blue-200 dark:border-blue-800 rounded-2xl p-6">
         <div className="flex flex-col sm:flex-row items-start sm:items-center justify-between gap-4">
           <div>
             <h3 className="text-lg font-bold text-gray-900 dark:text-white mb-2 flex items-center gap-2">