Remove legacy authentication and PostgreSQL configuration

- Remove obsolete auth middleware references from settings and notifications pages
- Clean up .env.example: remove unused PostgreSQL and PostgREST variables
- Delete POSTGRES_SETUP.md: outdated documentation for removed services
- App now uses Supabase directly instead of local PostgreSQL+PostgREST
- Authentication is handled entirely by Authentik Forward Auth at Traefik level

nuxt4-app/app/pages/settings.vue

@@ -1,6 +1,7 @@
 <script setup lang="ts">
 definePageMeta({
-  middleware: 'auth'
+  layout: 'dashboard',
+  title: 'Configuración'
 })
 </script>