fix(ui): replace dlgs dialogs with zenity

[SergioChan]

Summary

• replace github.com/gen2brain/dlgs with github.com/ncruces/zenity in the GUI dialog wrapper (pkg/ui/dlgs.go)
• preserve existing wrapper semantics for callers (bool,error and string,bool,error), including mapping canceled dialogs to ok=false without surfacing an error
• update dependency guard allowlist to permit github.com/ncruces/zenity
• Closes dlgs is dead #608.

Validation

• go test ./pkg/ui
• go test ./pkg/unpackerr -run TestDoesNotExist
• GOOS=windows GOARCH=amd64 go test ./pkg/ui
• git diff --check

Notes

• GOOS=darwin GOARCH=amd64 go test ./pkg/ui currently fails in this Windows environment due to existing github.com/getlantern/systray darwin build limitations (nativeLoop/registerSystray unresolved). The zenity wrapper changes compile and test on native host + windows cross-compile.

[davidnewhall]

Thanks for this. Saves me a few tokens.

GOOS=darwin GOARCH=amd64 go test ./pkg/ui currently fails in this Windows environment

That's fully expected and why the official build uses macOS and not a cross-compile - it doesn't work. Perhaps I'll find a better systray library to make this better. something like this github.com/energye/systray