auto_pair_device always patches gateway.controlUi.allowedOrigins. The
previous implementation saved the entire config snapshot captured at read
time, which could clobber concurrent user edits to gateway auth, models,
or channels when WebSocket auto-pair ran during reconnect.
Write only the allowedOrigins delta through the existing merge path so
other fields on disk are preserved.
Co-authored-by: 晴天 <1186258278@users.noreply.github.com>