feat(shared): Länderauswahl mit ISO 3166-1 Mapping und CountryPicker

Backend: Country-Record (Shared Kernel), InMemoryCountryRepository mit
~249 Ländern und DACH-Priorisierung, ListCountries-UseCase,
GET /api/countries?q= Endpoint.

Frontend: CountryPicker-Komponente mit Fuzzy-Suche, DACH-Favoriten bei
leerem Query. SupplierCreate-, CustomerCreate- und AddDeliveryAddress-
Screens verwenden jetzt den CountryPicker statt Freitext. Detail-Screens
zeigen den Ländercode in der Adressanzeige.

Closes #71

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

@@ -1,14 +1,16 @@
-import React, { useState } from 'react';
+import React, { useEffect, useState } from 'react';
 import { Box, Text, useInput } from 'ink';
-import type { CustomerType } from '@effigenix/api-client';
+import type { CustomerType, CountryDTO } from '@effigenix/api-client';
 import { useNavigation } from '../../../state/navigation-context.js';
 import { useCustomers } from '../../../hooks/useCustomers.js';
 import { FormInput } from '../../shared/FormInput.js';
+import { CountryPicker } from '../../shared/CountryPicker.js';
 import { LoadingSpinner } from '../../shared/LoadingSpinner.js';
 import { ErrorDisplay } from '../../shared/ErrorDisplay.js';
+import { client } from '../../../utils/api-client.js';
 
-type Field = 'name' | 'phone' | 'email' | 'street' | 'houseNumber' | 'postalCode' | 'city' | 'country' | 'paymentDueDays';
-const FIELDS: Field[] = ['name', 'phone', 'email', 'street', 'houseNumber', 'postalCode', 'city', 'country', 'paymentDueDays'];
+type Field = 'name' | 'phone' | 'email' | 'street' | 'houseNumber' | 'postalCode' | 'city' | 'countryPicker' | 'paymentDueDays';
+const FIELDS: Field[] = ['name', 'phone', 'email', 'street', 'houseNumber', 'postalCode', 'city', 'countryPicker', 'paymentDueDays'];
 
 const FIELD_LABELS: Record<Field, string> = {
   name: 'Name *',
@@ -18,7 +20,7 @@ const FIELD_LABELS: Record<Field, string> = {
   houseNumber: 'Hausnummer *',
   postalCode: 'PLZ *',
   city: 'Stadt *',
-  country: 'Land *',
+  countryPicker: 'Land *',
   paymentDueDays: 'Zahlungsziel (Tage)',
 };
 
@@ -28,15 +30,23 @@ export function CustomerCreateScreen() {
   const { replace, back } = useNavigation();
   const { createCustomer, loading, error, clearError } = useCustomers();
 
-  const [values, setValues] = useState<Record<Field, string>>({
+  const [values, setValues] = useState<Record<Exclude<Field, 'countryPicker'>, string>>({
     name: '', phone: '', email: '', street: '', houseNumber: '',
-    postalCode: '', city: '', country: 'Deutschland', paymentDueDays: '',
+    postalCode: '', city: '', paymentDueDays: '',
   });
   const [typeIndex, setTypeIndex] = useState(0);
   const [activeField, setActiveField] = useState<Field | 'type'>('name');
   const [fieldErrors, setFieldErrors] = useState<Partial<Record<Field | 'type', string>>>({});
+  const [countryQuery, setCountryQuery] = useState('');
+  const [countryCode, setCountryCode] = useState('DE');
+  const [countryName, setCountryName] = useState('Deutschland');
+  const [countries, setCountries] = useState<CountryDTO[]>([]);
 
-  const setField = (field: Field) => (value: string) => {
+  useEffect(() => {
+    client.countries.search().then(setCountries).catch(() => {});
+  }, []);
+
+  const setField = (field: Exclude<Field, 'countryPicker'>) => (value: string) => {
     setValues((v) => ({ ...v, [field]: value }));
   };
 
@@ -75,7 +85,6 @@ export function CustomerCreateScreen() {
     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;
 
@@ -87,7 +96,7 @@ export function CustomerCreateScreen() {
       houseNumber: values.houseNumber.trim(),
       postalCode: values.postalCode.trim(),
       city: values.city.trim(),
-      country: values.country.trim(),
+      country: countryCode,
       ...(values.email.trim() ? { email: values.email.trim() } : {}),
       ...(values.paymentDueDays.trim() ? { paymentDueDays: parseInt(values.paymentDueDays, 10) } : {}),
     });
@@ -122,17 +131,41 @@ export function CustomerCreateScreen() {
           {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] } : {})}
-          />
-        ))}
+        {FIELDS.map((field) => {
+          if (field === 'countryPicker') {
+            return (
+              <CountryPicker
+                key="countryPicker"
+                countries={countries}
+                query={countryQuery}
+                onQueryChange={setCountryQuery}
+                onSelect={(c) => {
+                  setCountryCode(c.code);
+                  setCountryName(c.name);
+                  setCountryQuery('');
+                  const idx = FIELDS.indexOf('countryPicker');
+                  if (idx < FIELDS.length - 1) {
+                    setActiveField(FIELDS[idx + 1] ?? 'countryPicker');
+                  }
+                }}
+                focus={activeField === 'countryPicker'}
+                selectedName={countryName}
+              />
+            );
+          }
+          const f = field as Exclude<Field, 'countryPicker'>;
+          return (
+            <FormInput
+              key={f}
+              label={FIELD_LABELS[f]}
+              value={values[f]}
+              onChange={setField(f)}
+              onSubmit={handleFieldSubmit(f)}
+              focus={activeField === f}
+              {...(fieldErrors[f] ? { error: fieldErrors[f] } : {})}
+            />
+          );
+        })}
       </Box>
 
       <Box marginTop={1}>