Add modular group verification system with frontend and backend checks

This commit implements a comprehensive, reusable group verification system:

Components:
- GroupCheckButton: Base component for group verification
- 7 specialized buttons: 3 real groups (authentik Admins, grupo-prueba, lvl0), 1 public access test, 2 system verification buttons
- All buttons support both frontend and backend verification modes

Backend:
- New API endpoint /api/auth/check-group for server-side group validation
- Reads Authentik headers and validates group membership

Frontend:
- Enhanced useAuthentik composable with hasGroup() and checkGroupBackend() methods
- Toast notifications for all verification results
- Smooth animations and color-coded visual feedback

UI Improvements:
- Organized layout with cards for different verification types
- Grid layout for group buttons
- Professional styling with hover effects and shadows
- Clear visual distinction between frontend/backend checks

nuxt4/server/api/auth/check-group.post.ts

@@ -0,0 +1,40 @@
+/**
+ * Endpoint para verificar membresía de grupo desde el backend
+ * Valida contra los headers de Authentik en el servidor
+ */
+export default defineEventHandler(async (event) => {
+  // Leer el body de la petición
+  const body = await readBody(event)
+  const { groupName } = body
+
+  if (!groupName || typeof groupName !== 'string') {
+    throw createError({
+      statusCode: 400,
+      statusMessage: 'Group name is required'
+    })
+  }
+
+  // Leer headers de Authentik
+  const headers = getHeaders(event)
+  const authentikGroups = headers['x-authentik-groups']
+
+  // Si no hay header de grupos, el usuario no está autenticado o no tiene grupos
+  if (!authentikGroups) {
+    return {
+      hasGroup: false,
+      groups: []
+    }
+  }
+
+  // Parsear los grupos (separados por |)
+  const userGroups = authentikGroups.split('|').filter(g => g.trim())
+
+  // Verificar si el usuario tiene el grupo solicitado
+  const hasGroup = userGroups.includes(groupName)
+
+  return {
+    hasGroup,
+    groups: userGroups,
+    checkedGroup: groupName
+  }
+})