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/validate.go

@@ -10,7 +10,7 @@ var hostnameRe = regexp.MustCompile(`^[a-zA-Z0-9]([a-zA-Z0-9-]{0,61}[a-zA-Z0-9])
 
 func validateHostname(name string) error {
 	if !hostnameRe.MatchString(name) {
-		return fmt.Errorf("ungültiger Hostname %q (nur Buchstaben, Ziffern, Bindestrich, kein führender/abschließender Bindestrich, keine Domain)", name)
+		return fmt.Errorf("invalid hostname %q (letters, digits, hyphen only; no leading/trailing hyphen; no domain)", name)
 	}
 	return nil
 }
@@ -26,23 +26,23 @@ func ip4ToUint32(ip net.IP) uint32 {
 func validateIP(ip, lanCIDR, poolStart, poolEnd string) error {
 	parsed := net.ParseIP(ip)
 	if parsed == nil || parsed.To4() == nil {
-		return fmt.Errorf("ungültige IPv4-Adresse: %q", ip)
+		return fmt.Errorf("invalid IPv4 address: %q", ip)
 	}
 	_, cidr, err := net.ParseCIDR(lanCIDR)
 	if err != nil {
-		return fmt.Errorf("internes Problem: ungültiges LAN-CIDR %q: %w", lanCIDR, err)
+		return fmt.Errorf("internal error: invalid LAN CIDR %q: %w", lanCIDR, err)
 	}
 	if !cidr.Contains(parsed) {
-		return fmt.Errorf("IP %s liegt nicht im LAN-Netz %s", ip, lanCIDR)
+		return fmt.Errorf("IP %s is not inside LAN network %s", ip, lanCIDR)
 	}
 	start := net.ParseIP(poolStart)
 	end := net.ParseIP(poolEnd)
 	if start == nil || end == nil {
-		return fmt.Errorf("internes Problem: ungültiger DHCP-Pool %q-%q", poolStart, poolEnd)
+		return fmt.Errorf("internal error: invalid DHCP pool %q-%q", poolStart, poolEnd)
 	}
 	v, s, e := ip4ToUint32(parsed), ip4ToUint32(start), ip4ToUint32(end)
 	if v >= s && v <= e {
-		return fmt.Errorf("IP %s liegt im dynamischen DHCP-Pool (%s-%s) und ist für statische Reservierungen gesperrt", ip, poolStart, poolEnd)
+		return fmt.Errorf("IP %s is inside the dynamic DHCP pool (%s-%s) and is reserved, not allowed for static assignments", ip, poolStart, poolEnd)
 	}
 	return nil
 }
@@ -55,7 +55,7 @@ func normalizeMAC(mac string) (string, error) {
 	}
 	hw, err := net.ParseMAC(mac)
 	if err != nil {
-		return "", fmt.Errorf("ungültige MAC-Adresse %q: %w", mac, err)
+		return "", fmt.Errorf("invalid MAC address %q: %w", mac, err)
 	}
 	return hw.String(), nil
 }