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/articles/AddSalesUnitScreen.tsx

@@ -0,0 +1,91 @@
+import React, { useState } from 'react';
+import { Box, Text, useInput } from 'ink';
+import type { Unit, PriceModel } from '@effigenix/api-client';
+import { UNIT_LABELS, PRICE_MODEL_LABELS } from '@effigenix/api-client';
+import { useNavigation } from '../../../state/navigation-context.js';
+import { useArticles } from '../../../hooks/useArticles.js';
+import { FormInput } from '../../shared/FormInput.js';
+import { LoadingSpinner } from '../../shared/LoadingSpinner.js';
+import { ErrorDisplay } from '../../shared/ErrorDisplay.js';
+
+const UNITS: Unit[] = ['PIECE_FIXED', 'KG', 'HUNDRED_GRAM', 'PIECE_VARIABLE'];
+const UNIT_PRICE_MODEL: Record<Unit, PriceModel> = {
+  PIECE_FIXED: 'FIXED',
+  KG: 'WEIGHT_BASED',
+  HUNDRED_GRAM: 'WEIGHT_BASED',
+  PIECE_VARIABLE: 'WEIGHT_BASED',
+};
+
+export function AddSalesUnitScreen() {
+  const { params, navigate, back } = useNavigation();
+  const articleId = params['articleId'] ?? '';
+  const { addSalesUnit, loading, error, clearError } = useArticles();
+
+  const [unitIndex, setUnitIndex] = useState(0);
+  const [price, setPrice] = useState('');
+  const [activeField, setActiveField] = useState<'unit' | 'price'>('unit');
+  const [priceError, setPriceError] = useState<string | null>(null);
+
+  const selectedUnit = UNITS[unitIndex] ?? 'PIECE_FIXED';
+  const autoModel = UNIT_PRICE_MODEL[selectedUnit];
+
+  useInput((_input, key) => {
+    if (loading) return;
+
+    if (activeField === 'unit') {
+      if (key.leftArrow) setUnitIndex((i) => Math.max(0, i - 1));
+      if (key.rightArrow) setUnitIndex((i) => Math.min(UNITS.length - 1, i + 1));
+      if (key.tab || key.downArrow || key.return) setActiveField('price');
+    }
+
+    if (key.upArrow && activeField === 'price') setActiveField('unit');
+    if (key.escape) back();
+  });
+
+  const handleSubmit = async () => {
+    const priceNum = parseFloat(price.replace(',', '.'));
+    if (isNaN(priceNum) || priceNum <= 0) {
+      setPriceError('Gültiger Preis erforderlich.');
+      return;
+    }
+    setPriceError(null);
+    const updated = await addSalesUnit(articleId, { unit: selectedUnit, priceModel: autoModel, price: priceNum });
+    if (updated) navigate('article-detail', { articleId });
+  };
+
+  if (loading) return <Box paddingY={2}><LoadingSpinner label="Verkaufseinheit wird hinzugefügt..." /></Box>;
+
+  return (
+    <Box flexDirection="column" gap={1}>
+      <Text color="cyan" bold>Verkaufseinheit hinzufügen</Text>
+      {error && <ErrorDisplay message={error} onDismiss={clearError} />}
+
+      <Box flexDirection="column" gap={1} width={60}>
+        <Box flexDirection="column">
+          <Text color={activeField === 'unit' ? 'cyan' : 'gray'}>Einheit *</Text>
+          <Box gap={1}>
+            <Text color={activeField === 'unit' ? 'cyan' : 'gray'}>{'< '}</Text>
+            <Text color={activeField === 'unit' ? 'white' : 'gray'}>{UNIT_LABELS[selectedUnit]}</Text>
+            <Text color={activeField === 'unit' ? 'cyan' : 'gray'}>{' >'}</Text>
+            <Text color="gray" dimColor>→ {PRICE_MODEL_LABELS[autoModel]}</Text>
+          </Box>
+          {activeField === 'unit' && <Text color="gray" dimColor>←→ Einheit · Tab/Enter weiter</Text>}
+        </Box>
+
+        <FormInput
+          label="Preis (€) *"
+          value={price}
+          onChange={setPrice}
+          onSubmit={() => void handleSubmit()}
+          focus={activeField === 'price'}
+          placeholder="z.B. 2.49"
+          {...(priceError ? { error: priceError } : {})}
+        />
+      </Box>
+
+      <Box marginTop={1}>
+        <Text color="gray" dimColor>Tab/↑↓ Feld · ←→ Einheit · Enter speichern · Escape Abbrechen</Text>
+      </Box>
+    </Box>
+  );
+}