ui(save-as): label the version-dialog button "Continue"

On native the button opens the OS save dialog (folder + name + overwrite)
and on web it starts the download, so it does not itself save — "Continue"
reads truer than "Save".

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/view/modal.rs

@@ -777,7 +777,7 @@ fn save_as_dialog_window<'a>(filename: &'a str, format: &'a str) -> Element<'a,
     items.push(
         row![
             Space::new().width(Fill),
-            btn("Save", Message::SaveDialogConfirm, BTN_OK, BTN_HOV),
+            btn("Continue", Message::SaveDialogConfirm, BTN_OK, BTN_HOV),
             Space::new().width(8),
             btn("Cancel", Message::SaveDialogCancel, BTN_GREY, BTN_GHOV),
         ]