Raylux 0.31.2: device passwords join the credential store

Closes the gap 0.31.1 shipped with.

Device credentials

0.31.1 moved six credential fields into the protected store but left one known gap: a device password edited through the gateway interface was still written in clear text.

• A device password saved through the interface now goes to the credential store, reusing the entry migration created rather than duplicating it.
• Reading one back returns a mask. Before this, it returned whatever was stored — including clear text on a hand-edited configuration.
• A rotated password reaches the live device without a restart, and switching a device to another protocol erases its stored entry.
• A credential on an unencrypted connection is no longer dropped — it is sent, with a warning that it travels unencrypted.

Fixes

• Studio's Add Connection dialog accepts host:port and pasted addresses. It joined the address verbatim, so the form the manual itself recommends failed with a doubled port number. A failed check now keeps what you typed so you can correct it.

Known limitations at this release

• Polling drivers do not use a device password; only OPC UA connections read it. Saving one on another driver is now refused rather than stored where it does nothing.