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

frontend/src/components/LlamadorAPI.tsx

@@ -10,6 +10,7 @@ import {
   Group,
 } from '@mantine/core';
 import { MetodoSelect } from './MetodoSelect';
+import { useMantineTheme } from '@mantine/core';
 
 export function LlamadorAPI() {
   const [direccion, setDireccion] = useState('http://localhost:8000/api/saludo');
@@ -25,6 +26,9 @@ export function LlamadorAPI() {
     return 'red';
   };
 
+  const theme = useMantineTheme();
+  
+
   const llamarAPI = async () => {
     try {
       const options: RequestInit = {
@@ -101,7 +105,12 @@ export function LlamadorAPI() {
             minRows={3}
           />
 
-          <Button onClick={llamarAPI} color="blue">
+          <Button onClick={llamarAPI} 
+          variant="gradient"
+          gradient={{
+                  from: theme.colors.brand[7],
+                  to: theme.colors.brand[4],
+                }}>
             Enviar solicitud
           </Button>