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/host.go

@@ -22,7 +22,7 @@ const hostHeader = "# ipadm host database - managed with `ipadm`, do not edit wh
 func parseHostLine(line string) (Host, error) {
 	parts := strings.SplitN(line, "\t", 4)
 	if len(parts) < 3 {
-		return Host{}, fmt.Errorf("ungültige Zeile (erwarte mind. 3 Tab-getrennte Felder): %q", line)
+		return Host{}, fmt.Errorf("invalid line (expected at least 3 tab-separated fields): %q", line)
 	}
 	mac := parts[2]
 	if mac == "-" {