settings tab rework

[objz]

what would you like

Rework the settings panel once the final groups and controls are clear.

current follow-up from #31

• give content-provider preferences a proper settings UI
• keep build-provided credentials out of the editable user settings
• group discovery behavior separately from instance defaults
• preserve keyboard navigation and the compact popup styling

The discovery and update work does not redesign this tab. It only leaves the provider behavior ready for the later settings rework.