In production (WG_WG_ENABLED=true), on_device_created() runs multiple
WG and nftables subprocess calls that take seconds. The UI handler
was awaiting all of them before showing the config dialog, causing
WebSocket timeouts and page reloads.
Now the dialog/QR/download appears right after DB commit, and WG peer
+ firewall configuration runs as a background task via asyncio.create_task.
a8784eec9c