feat(fasting): 新增轻断食功能模块

新增完整的轻断食功能，包括：
- 断食计划列表和详情页面，支持12-12、14-10、16-8、18-6四种计划
- 断食状态实时追踪和倒计时显示
- 自定义开始时间选择器
- 断食通知提醒功能
- Redux状态管理和数据持久化
- 新增tab导航入口和路由配置

app/(tabs)/_layout.tsx

@@ -21,6 +21,7 @@ type TabConfig = {
 
 const TAB_CONFIGS: Record<string, TabConfig> = {
   statistics: { icon: 'chart.pie.fill', title: '健康' },
+  fasting: { icon: 'timer', title: '断食' },
   goals: { icon: 'flag.fill', title: '习惯' },
   challenges: { icon: 'trophy.fill', title: '挑战' },
   personal: { icon: 'person.fill', title: '个人' },
@@ -36,6 +37,7 @@ export default function TabLayout() {
   const isTabSelected = (routeName: string): boolean => {
     const routeMap: Record<string, string> = {
       statistics: ROUTES.TAB_STATISTICS,
+      fasting: ROUTES.TAB_FASTING,
       goals: ROUTES.TAB_GOALS,
       challenges: ROUTES.TAB_CHALLENGES,
       personal: ROUTES.TAB_PERSONAL,
@@ -176,6 +178,10 @@ export default function TabLayout() {
         <Label>健康</Label>
         <Icon sf="chart.pie.fill" drawable="custom_android_drawable" />
       </NativeTabs.Trigger>
+      <NativeTabs.Trigger name="fasting">
+        <Icon sf="timer" drawable="custom_android_drawable" />
+        <Label>断食</Label>
+      </NativeTabs.Trigger>
       <NativeTabs.Trigger name="goals">
         <Icon sf="flag.fill" drawable="custom_settings_drawable" />
         <Label>习惯</Label>
@@ -198,6 +204,7 @@ export default function TabLayout() {
     >
 
       <Tabs.Screen name="statistics" options={{ title: '健康' }} />
+      <Tabs.Screen name="fasting" options={{ title: '断食' }} />
       <Tabs.Screen name="goals" options={{ title: '习惯' }} />
       <Tabs.Screen name="challenges" options={{ title: '挑战' }} />
       <Tabs.Screen name="personal" options={{ title: '个人' }} />