fix(accounts): simplify identity copy tooltips

Show only the copy action in populated username and email cell tooltips instead of repeating values already visible in the table. Preserve explicit accessible button labels and add German and English regression coverage.

src/renderer/views/settings/AccountWorkspace.tsx

@@ -142,7 +142,7 @@ function renderAccountIdentityCell({
 }): ReactElement {
   const copyable = value.trim() !== "" && value !== "—";
   return (
-    <span className={className} role="cell" title={copyable ? `${value}\nKlicken zum Kopieren` : value}>
+    <span className={className} role="cell" title={copyable ? "Klicken zum Kopieren" : value}>
       {copyable ? (
         <button
           aria-label={`${label} kopieren`}