feat(challenges): 添加自定义挑战类型并优化字段验证

- 新增 CUSTOM 挑战类型支持
- 移除 requirementLabel 必填验证，改为可选字段
- 添加挑战类型选择器的编辑模式禁用状态
- 优化日期选择器的多语言支持
- 完善中英文国际化文案
- 修复空 requirementLabel 导致的渲染问题

app/challenges/create-custom.tsx

@@ -1,3 +1,4 @@
+import i18n from '@/i18n';
 import dayjs from 'dayjs';
 import { BlurView } from 'expo-blur';
 import * as Clipboard from 'expo-clipboard';
@@ -53,6 +54,7 @@ const getTypeOptions = (t: (key: string) => string): { value: ChallengeType; lab
   { value: ChallengeType.SLEEP, label: t('challenges.createCustom.typeLabels.sleep'), accent: '#7C3AED' },
   { value: ChallengeType.MOOD, label: t('challenges.createCustom.typeLabels.mood'), accent: '#F97316' },
   { value: ChallengeType.WEIGHT, label: t('challenges.createCustom.typeLabels.weight'), accent: '#22C55E' },
+  { value: ChallengeType.CUSTOM, label: t('challenges.createCustom.typeLabels.custom'), accent: '#8B5CF6' },
 ];
 
 const FALLBACK_IMAGE =
@@ -97,7 +99,7 @@ export default function CreateCustomChallengeScreen() {
   const [progressUnit, setProgressUnit] = useState('');
   const [periodLabel, setPeriodLabel] = useState('');
   const [periodEdited, setPeriodEdited] = useState(false);
-  const [rankingDescription] = useState('连续打卡榜');
+  const [rankingDescription] = useState(t('challenges.createCustom.rankingDescription'));
   const [isPublic, setIsPublic] = useState(true);
   const [maxParticipants, setMaxParticipants] = useState('100');
   const [minimumEdited, setMinimumEdited] = useState(false);
@@ -121,7 +123,6 @@ export default function CreateCustomChallengeScreen() {
         setEndDate(new Date(challenge.endAt || Date.now()));
         setTargetValue(String(challenge.progress?.target || ''));
         setMinimumCheckInDays(String(challenge.minimumCheckInDays || ''));
-        setRequirementLabel(challenge.requirementLabel || '');
         setSummary(challenge.summary || '');
         setProgressUnit(challenge.unit || '');
         setPeriodLabel(challenge.periodLabel || '');
@@ -177,10 +178,6 @@ export default function CreateCustomChallengeScreen() {
       return;
     }
 
-    if (!requirementLabel.trim()) {
-      Toast.warning(t('challenges.createCustom.alerts.requirementRequired'));
-      return;
-    }
 
     const startTimestamp = dayjs(startDate).valueOf();
     const endTimestamp = dayjs(endDate).valueOf();
@@ -221,7 +218,7 @@ export default function CreateCustomChallengeScreen() {
       targetValue: target,
       minimumCheckInDays: minDays,
       durationLabel,
-      requirementLabel: requirementLabel.trim(),
+      requirementLabel: '',
       summary: summary.trim() || undefined,
       progressUnit: progressUnit.trim(),
       periodLabel: periodLabel.trim() || undefined,
@@ -513,16 +510,19 @@ export default function CreateCustomChallengeScreen() {
                     <TouchableOpacity
                       key={option.value}
                       activeOpacity={0.9}
-                      onPress={() => setType(option.value)}
+                      onPress={() => !isEditMode && setType(option.value)}
+                      disabled={isEditMode}
                       style={[
                         styles.chip,
                         active && { backgroundColor: `${option.accent}1A`, borderColor: option.accent },
+                        isEditMode && styles.chipDisabled,
                       ]}
                     >
                       <Text
                         style={[
                           styles.chipLabel,
                           active && { color: option.accent, fontWeight: '700' },
+                          isEditMode && styles.chipLabelDisabled,
                         ]}
                       >
                         {option.label}
@@ -531,6 +531,7 @@ export default function CreateCustomChallengeScreen() {
                   );
                 })}
               </View>
+              <Text style={styles.helperText}>{t('challenges.createCustom.fields.challengeTypeHelper')}</Text>
             </View>
 
             <View style={styles.fieldBlock}>
@@ -592,7 +593,6 @@ export default function CreateCustomChallengeScreen() {
 
             {renderField(t('challenges.createCustom.fields.minimumCheckInDays'), minimumCheckInDays, handleMinimumDaysChange, t('challenges.createCustom.fields.minimumCheckInDaysPlaceholder'), 'numeric')}
 
-            {renderField(t('challenges.createCustom.fields.challengeRequirement'), requirementLabel, setRequirementLabel, t('challenges.createCustom.fields.requirementPlaceholder'))}
           </View>
 
           <View style={styles.formCard}>
@@ -675,6 +675,9 @@ export default function CreateCustomChallengeScreen() {
         minimumDate={pickerType === 'end' ? dayjs(startDate).add(1, 'day').toDate() : dayjs().add(1, 'day').toDate()}
         onConfirm={handleConfirmDate}
         onCancel={() => setPickerType(null)}
+        locale={i18n.language}
+        confirmTextIOS={t('challenges.createCustom.datePicker.confirm')}
+        cancelTextIOS={t('challenges.createCustom.datePicker.cancel')}
       />
 
       <Modal
@@ -833,10 +836,17 @@ const styles = StyleSheet.create({
     borderWidth: 1,
     borderColor: '#e5e7eb',
   },
+  chipDisabled: {
+    opacity: 0.5,
+    backgroundColor: '#f1f5f9',
+  },
   chipLabel: {
     fontSize: 13,
     color: '#334155',
   },
+  chipLabelDisabled: {
+    color: '#94a3b8',
+  },
   uploadRow: {
     flexDirection: 'row',
     alignItems: 'center',