refactor(sleep): 重构睡眠数据获取逻辑，移除冗余代码并优化组件结构

- 从 healthSlice 和 health.ts 中移除 sleepDuration 字段及相关获取逻辑
- 将 SleepCard 改为按需异步获取睡眠数据，支持传入指定日期
- 睡眠详情页改为通过路由参数接收日期，支持查看历史记录
- 移除 statistics 页面对 sleepDuration 的直接依赖，统一由 SleepCard 管理
- 删除未使用的 SleepStageChart 组件，简化页面结构

app/(tabs)/statistics.tsx

@@ -98,7 +98,6 @@ export default function ExploreScreen() {
   const hourlySteps = useMockData ? (mockData?.hourlySteps ?? []) : (healthData?.hourlySteps ?? []);
   const activeCalories = useMockData ? (mockData?.activeEnergyBurned ?? null) : (healthData?.activeEnergyBurned ?? null);
   const basalMetabolism: number | null = useMockData ? (mockData?.basalEnergyBurned ?? null) : (healthData?.basalEnergyBurned ?? null);
-  const sleepDuration = useMockData ? (mockData?.sleepDuration ?? null) : (healthData?.sleepDuration ?? null);
   const hrvValue = useMockData ? (mockData?.hrv ?? null) : (healthData?.hrv ?? null);
   const oxygenSaturation = useMockData ? (mockData?.oxygenSaturation ?? null) : (healthData?.oxygenSaturation ?? null);
 
@@ -293,7 +292,6 @@ export default function ExploreScreen() {
             steps: data.steps,
             activeCalories: data.activeEnergyBurned,
             basalEnergyBurned: data.basalEnergyBurned,
-            sleepDuration: data.sleepDuration,
             hrv: data.hrv,
             oxygenSaturation: data.oxygenSaturation,
             heartRate: data.heartRate,
@@ -587,9 +585,9 @@ export default function ExploreScreen() {
             </FloatingCard> */}
 
             <FloatingCard style={styles.masonryCard}>
-              <SleepCard 
-                sleepDuration={sleepDuration} 
-                onPress={() => pushIfAuthedElseLogin('/sleep-detail')}
+              <SleepCard
+                selectedDate={currentSelectedDate}
+                onPress={() => pushIfAuthedElseLogin(`/sleep-detail?date=${dayjs(currentSelectedDate).format('YYYY-MM-DD')}`)}
               />
             </FloatingCard>
           </View>