ipadm: translate to English, fix help alignment

- All ipadm-internal messages (usage, prompts, errors) are now English
- Usage text is built programmatically from a (left, desc) row list with
  computed column width instead of hand-aligned spaces, so it can't drift
  out of alignment again when rows are added/changed
- README's literal usage block updated to match; rest of the repo docs
  stay German

tools/ipadm/store.go

@@ -21,15 +21,15 @@ type LineStore[T any] struct {
 
 func openLineStore[T any](path, header string, parse func(string) (T, error), format func(T) string) (*LineStore[T], error) {
 	if err := os.MkdirAll(dirOf(path), 0755); err != nil {
-		return nil, fmt.Errorf("kann Verzeichnis für %s nicht anlegen: %w", path, err)
+		return nil, fmt.Errorf("cannot create directory for %s: %w", path, err)
 	}
 	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0644)
 	if err != nil {
-		return nil, fmt.Errorf("kann %s nicht öffnen: %w", path, err)
+		return nil, fmt.Errorf("cannot open %s: %w", path, err)
 	}
 	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX); err != nil {
 		f.Close()
-		return nil, fmt.Errorf("kann Lock auf %s nicht setzen: %w", path, err)
+		return nil, fmt.Errorf("cannot lock %s: %w", path, err)
 	}
 	return &LineStore[T]{path: path, file: f, header: header, parse: parse, format: format}, nil
 }