Fix useAuthentik composable for SSR

- Use useState to pass server headers to client
- Fix 'useAuthentik is not defined' error
- Ensure headers are read only on server side

nuxt4/composables/useAuthentik.ts

@@ -3,9 +3,12 @@
  * Los headers son inyectados por Authentik Proxy Outpost
  */
 export const useAuthentik = () => {
+  // Leer headers en el servidor y almacenarlos en state
+  const authentikUser = useState('authentikUser', () => {
+    // Solo en el servidor, leer los headers
+    if (process.server) {
       const headers = useRequestHeaders()
 
-  const user = computed(() => {
       const username = headers['x-authentik-username']
       const email = headers['x-authentik-email']
       const name = headers['x-authentik-name']
@@ -26,8 +29,12 @@ export const useAuthentik = () => {
         // Generar avatar URL usando UI Avatars
         avatar: `https://ui-avatars.com/api/?name=${encodeURIComponent(name || username)}&background=random&size=128`
       }
+    }
+
+    return null
   })
 
+  const user = computed(() => authentikUser.value)
   const isAuthenticated = computed(() => !!user.value)
 
   const logout = () => {