fix: use Docker container name for Metabase internal communication

Change Metabase URL from public domain to Docker container name
for proper internal network communication between containers.

Changes:
- Update default METABASE_URL to http://metabase:3000
- Docker DNS resolution works correctly with container names
- Maintains public domain fallback via environment variables

This fixes authentication issues when containers communicate
within the same Docker network.

.env.example

@@ -2,6 +2,7 @@
 NUXT_PUBLIC_AUTHENTIK_URL=https://authentik.nucleoriofrio.com
 
 # Metabase Configuration (server-side only)
-METABASE_URL=https://metabase.nucleoriofrio.com
+# Use container name for Docker internal communication
+METABASE_URL=http://metabase:3000
 METABASE_EMAIL=your-email@domain.com
 METABASE_PASSWORD=your-password