feat: Refactor styling and theme integration across components; update button gradients and remove unused component

frontend/src/pages/404.tsx

@@ -1,10 +1,16 @@
 import { Box, Title, Text, Button, Group, Stack, Image, Center } from '@mantine/core';
+import { useMantineTheme } from '@mantine/core';
 import { IconArrowLeft } from '../assets/icons';
 import { Link } from 'react-router-dom';
 import { MantineCardWithShader } from '../components/HoloShader'; // Ajusta ruta si es necesario
 import { AppShellWithMenu } from '../components/Appshell/Appshell';
 
+
 export function Error_404() {
+
+  const theme = useMantineTheme();
+
+
   return (
     <AppShellWithMenu>
       <Box
@@ -41,7 +47,10 @@ export function Error_404() {
                 to="/"
                 size="md"
                 variant="gradient"
-                gradient={{ from: 'blue', to: 'cyan' }}
+                gradient={{
+                  from: theme.colors.brand[7],
+                  to: theme.colors.secondary[4],
+                }}
                 leftSection={<IconArrowLeft width={18} height={18} />}
               >
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