ctx.open_url is unreliable on native (notably Windows), so the Help menu,
the Discord buttons, and the start-page links did nothing. Added an open_url
Service hook wired to the `open` crate on native (ShellExecute on Windows);
links::open prefers it and falls back to ctx.open_url (web). link_row now
routes clicks through it instead of ui.hyperlink_to. Test drives every Help
link id + the open() helper through a mock service.
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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