The station-control code rebuilt a fresh driver on every status poll and every
relay set. Stateful boards (Denkovi FTDI D2XX, USB-serial) hold an OS handle only
one opener can own, so the first poll opened the board and leaked the handle, and
every poll after failed with 'device in use' — the relays greyed out a second
after Save and auto-control never switched. Drivers are now cached per device and
reused, closed on config change. Adds a Test-connection button + detect feedback
in the device editor (reported by VK4MA).
rouggy