fix(ui): form dividers ignore the theme (black lines in the light theme) #1443

Problem

The connection forms use material.Divider(height: 1) with no colour, so the rules above and below the scrollable body are near-black in the light theme, while the rest of the app uses workbench.borderSubtle.

Scope

• A kit QueryaDivider (or a borderSubtle helper) and its use in the connection forms and other dialogs that call Divider directly.
• Guard: no bare material.Divider / Divider( outside the kit.

Found while driving a Linux debug build of dev after the button migration (UI consistency review). Part of epic #1331.