Fix VPN UI for active transient entries

[louzt]

Summary

Fixes the VPN UI empty-state behavior when the backend reports active VPN or tunnel connections that are not represented as importable profiles.

Fixes #2311

What changed

• Merge active VPN entries that are missing from the profiles list into the visible VPN model.
• Mark those entries as transient so the UI can show them without treating them like imported configs.
• Hide expand and delete actions for transient entries in both the control center popout and Settings.
• Preserve existing behavior for regular importable VPN profiles.

Validation

• QML diagnostics reported no errors on the touched files.
• Repository lint bootstrap succeeded, but the local lint-qml target could not complete in this environment because its qmllint wrapper resolves to a missing Qt5 path.

[louzt]

I noticed this bug while validating a self-hosted VPN workflow outside the normal UI import path.

In that setup, the backend state detection was already working correctly and the connection showed up as active, but the VPN UI still rendered the empty "No VPN profiles" state because it only reflected importable profile entries.

That made it easier to separate the problem into two parts:

• backend detection was already correct
• the UI model was treating importable profiles as the only visible source of truth

This PR is meant to address that UI-side gap without tying the fix to any specific provider or private setup.