feat(cli): Stammdaten-TUI mit Master Data API-Anbindung

- Neue Screens: Kategorien, Lieferanten, Artikel, Kunden (jeweils
  Liste, Detail, Anlegen + Detailaktionen wie Bewertung, Zertifikate,
  Verkaufseinheiten, Lieferadressen, Präferenzen)
- API-Client: Resources für alle 4 Stammdaten-Aggregate implementiert
  (categories, suppliers, articles, customers) mit Mapping von
  verschachtelten Domain-VOs auf flache DTOs
- Lieferant, Artikel, Kategorie: echte HTTP-Calls gegen Backend
  (/api/suppliers, /api/articles, /api/categories, /api/customers)
- 204-No-Content-Endpoints (removeSalesUnit, removeSupplier,
  removeCertificate, removeDeliveryAddress, removeFrameContract)
  lösen Re-Fetch des Aggregats aus
- MasterdataMenu, Navigation-Erweiterung, App.tsx-Routing

frontend/apps/cli/src/components/masterdata/customers/CustomerCreateScreen.tsx

@@ -0,0 +1,145 @@
+import React, { useState } from 'react';
+import { Box, Text, useInput } from 'ink';
+import type { CustomerType } from '@effigenix/api-client';
+import { useNavigation } from '../../../state/navigation-context.js';
+import { useCustomers } from '../../../hooks/useCustomers.js';
+import { FormInput } from '../../shared/FormInput.js';
+import { LoadingSpinner } from '../../shared/LoadingSpinner.js';
+import { ErrorDisplay } from '../../shared/ErrorDisplay.js';
+
+type Field = 'name' | 'phone' | 'email' | 'street' | 'houseNumber' | 'postalCode' | 'city' | 'country' | 'paymentDueDays';
+const FIELDS: Field[] = ['name', 'phone', 'email', 'street', 'houseNumber', 'postalCode', 'city', 'country', 'paymentDueDays'];
+
+const FIELD_LABELS: Record<Field, string> = {
+  name: 'Name *',
+  phone: 'Telefon *',
+  email: 'E-Mail',
+  street: 'Straße *',
+  houseNumber: 'Hausnummer *',
+  postalCode: 'PLZ *',
+  city: 'Stadt *',
+  country: 'Land *',
+  paymentDueDays: 'Zahlungsziel (Tage)',
+};
+
+const TYPES: CustomerType[] = ['B2B', 'B2C'];
+
+export function CustomerCreateScreen() {
+  const { navigate, back } = useNavigation();
+  const { createCustomer, loading, error, clearError } = useCustomers();
+
+  const [values, setValues] = useState<Record<Field, string>>({
+    name: '', phone: '', email: '', street: '', houseNumber: '',
+    postalCode: '', city: '', country: 'Deutschland', paymentDueDays: '',
+  });
+  const [typeIndex, setTypeIndex] = useState(0);
+  const [activeField, setActiveField] = useState<Field | 'type'>('name');
+  const [fieldErrors, setFieldErrors] = useState<Partial<Record<Field | 'type', string>>>({});
+
+  const setField = (field: Field) => (value: string) => {
+    setValues((v) => ({ ...v, [field]: value }));
+  };
+
+  useInput((_input, key) => {
+    if (loading) return;
+
+    if (activeField === 'type') {
+      if (key.leftArrow) setTypeIndex((i) => Math.max(0, i - 1));
+      if (key.rightArrow) setTypeIndex((i) => Math.min(TYPES.length - 1, i + 1));
+      if (key.tab || key.downArrow || key.return) setActiveField('name');
+    } else {
+      if (key.tab || key.downArrow) {
+        setActiveField((f) => {
+          if (f === 'type') return 'name';
+          const idx = FIELDS.indexOf(f as Field);
+          return FIELDS[(idx + 1) % FIELDS.length] ?? f;
+        });
+      }
+      if (key.upArrow) {
+        setActiveField((f) => {
+          if (f === 'type') return f;
+          const idx = FIELDS.indexOf(f as Field);
+          if (idx === 0) return 'type';
+          return FIELDS[idx - 1] ?? f;
+        });
+      }
+    }
+    if (key.escape) back();
+  });
+
+  const handleSubmit = async () => {
+    const errors: Partial<Record<Field | 'type', string>> = {};
+    if (!values.name.trim()) errors.name = 'Name ist erforderlich.';
+    if (!values.phone.trim()) errors.phone = 'Telefon ist erforderlich.';
+    if (!values.street.trim()) errors.street = 'Straße ist erforderlich.';
+    if (!values.houseNumber.trim()) errors.houseNumber = 'Hausnummer ist erforderlich.';
+    if (!values.postalCode.trim()) errors.postalCode = 'PLZ ist erforderlich.';
+    if (!values.city.trim()) errors.city = 'Stadt ist erforderlich.';
+    if (!values.country.trim()) errors.country = 'Land ist erforderlich.';
+    setFieldErrors(errors);
+    if (Object.keys(errors).length > 0) return;
+
+    const result = await createCustomer({
+      name: values.name.trim(),
+      type: TYPES[typeIndex] ?? 'B2B',
+      phone: values.phone.trim(),
+      street: values.street.trim(),
+      houseNumber: values.houseNumber.trim(),
+      postalCode: values.postalCode.trim(),
+      city: values.city.trim(),
+      country: values.country.trim(),
+      ...(values.email.trim() ? { email: values.email.trim() } : {}),
+      ...(values.paymentDueDays.trim() ? { paymentDueDays: parseInt(values.paymentDueDays, 10) } : {}),
+    });
+    if (result) navigate('customer-list');
+  };
+
+  const handleFieldSubmit = (field: Field) => (_value: string) => {
+    const idx = FIELDS.indexOf(field);
+    if (idx < FIELDS.length - 1) {
+      setActiveField(FIELDS[idx + 1] ?? field);
+    } else {
+      void handleSubmit();
+    }
+  };
+
+  if (loading) return <Box paddingY={2}><LoadingSpinner label="Kunde wird angelegt..." /></Box>;
+
+  return (
+    <Box flexDirection="column" gap={1}>
+      <Text color="cyan" bold>Neuer Kunde</Text>
+      {error && <ErrorDisplay message={error} onDismiss={clearError} />}
+
+      <Box flexDirection="column" gap={1} width={60}>
+        {/* Type Selector */}
+        <Box flexDirection="column">
+          <Text color={activeField === 'type' ? 'cyan' : 'gray'}>Typ *</Text>
+          <Box gap={1}>
+            <Text color={activeField === 'type' ? 'cyan' : 'gray'}>{'< '}</Text>
+            <Text color={activeField === 'type' ? 'white' : 'gray'}>{TYPES[typeIndex]}</Text>
+            <Text color={activeField === 'type' ? 'cyan' : 'gray'}>{' >'}</Text>
+          </Box>
+          {activeField === 'type' && <Text color="gray" dimColor>←→ Typ · Tab/Enter weiter</Text>}
+        </Box>
+
+        {FIELDS.map((field) => (
+          <FormInput
+            key={field}
+            label={FIELD_LABELS[field]}
+            value={values[field]}
+            onChange={setField(field)}
+            onSubmit={handleFieldSubmit(field)}
+            focus={activeField === field}
+            {...(fieldErrors[field] ? { error: fieldErrors[field] } : {})}
+          />
+        ))}
+      </Box>
+
+      <Box marginTop={1}>
+        <Text color="gray" dimColor>
+          Tab/↑↓ Feld · ←→ Typ · Enter auf letztem Feld speichern · Escape Abbrechen
+        </Text>
+      </Box>
+    </Box>
+  );
+}