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/dnsmasq.go

@@ -45,11 +45,11 @@ func applyDnsmasqConfig(path string, content string) error {
 		backup = b
 		hadFile = true
 	} else if !os.IsNotExist(err) {
-		return fmt.Errorf("kann bestehende %s nicht lesen: %w", path, err)
+		return fmt.Errorf("cannot read existing %s: %w", path, err)
 	}
 
 	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
-		return fmt.Errorf("kann %s nicht schreiben: %w", path, err)
+		return fmt.Errorf("cannot write %s: %w", path, err)
 	}
 
 	if err := runDnsmasqTest(); err != nil {
@@ -59,11 +59,11 @@ func applyDnsmasqConfig(path string, content string) error {
 		} else {
 			os.Remove(path)
 		}
-		return fmt.Errorf("dnsmasq-Konfiguration ungültig, Änderung zurückgerollt: %w", err)
+		return fmt.Errorf("dnsmasq config invalid, change rolled back: %w", err)
 	}
 
 	if err := reloadDnsmasq(); err != nil {
-		return fmt.Errorf("%s geschrieben, aber Reload fehlgeschlagen: %w", path, err)
+		return fmt.Errorf("%s written, but reload failed: %w", path, err)
 	}
 	return nil
 }