About/Help links: handle external URL open failures

[johnny9]

Code Gap

qml/components/ExternalPopup.qml calls Qt.openUrlExternally(externalConfirmPopup.link) and closes immediately. The return value is ignored, and there is no fallback if the OS/browser cannot open the URL.

qml/controls/ExternalLink.qml can also open links directly through Qt.openUrlExternally(link).

Work Needed

• Centralize external link opening behavior used by About/Help links.
• Check whether opening the URL succeeds.
• Keep the popup open or show an error when opening fails.
• Provide a copy-URL fallback.
• Ensure direct ExternalLink usage and popup-confirmed links behave consistently.
• Add tests or documented manual coverage for success and failure paths.

Priority

Preview / P1 because About/Help links are visible user-facing UI.