Backend: accept target_device_id — connect to target, enable btest
server, run test from source using target credentials, disable server
in finally (even on failure). Manual IP mode preserved as fallback.
Frontend: device picker dropdown (all managed devices except self) as
default mode; toggle to Manual IP for non-managed targets with a warning
that the server must be pre-enabled. Results show target IP in labels.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>