Google Drive backups

Google Drive (backups_pro)

1. panelze.com admin → Integrations — enter Google OAuth client ID/secret
2. Redirect URI: https://panelze.com/backups/google-callback
3. On the customer panel with backups_pro: Backups → Connect Google Drive
4. OAuth returns via panelze.com; tokens are forwarded to the panel

No per-server .env OAuth keys required when using the central hub.