feat(auth): 为未登录用户添加登录引导界面

为目标页面、营养记录、食物添加等功能添加登录状态检查和引导界面，确保用户在未登录状态下能够获得清晰的登录提示和指引。

- 在目标页面添加精美的未登录引导界面，包含渐变背景和登录按钮
- 为食物记录相关组件添加登录状态检查，未登录时自动跳转登录页面
- 重构血氧饱和度卡片为独立数据获取，移除对外部数据依赖
- 移除个人页面的实验性SwiftUI组件，统一使用原生TouchableOpacity
- 清理统计页面和营养记录页面的冗余代码和未使用变量

components/statistic/OxygenSaturationCard.tsx

@@ -1,32 +1,63 @@
-import React from 'react';
-import { StyleSheet } from 'react-native';
+import React, { useState, useCallback, useRef } from 'react';
+import { useFocusEffect } from '@react-navigation/native';
 import HealthDataCard from './HealthDataCard';
+import { fetchOxygenSaturation } from '@/utils/health';
+import dayjs from 'dayjs';
 
 interface OxygenSaturationCardProps {
-  resetToken: number;
   style?: object;
-  oxygenSaturation?: number | null;
+  selectedDate?: Date;
 }
 
 const OxygenSaturationCard: React.FC<OxygenSaturationCardProps> = ({
-  resetToken,
   style,
-  oxygenSaturation
+  selectedDate
 }) => {
+  const [oxygenSaturation, setOxygenSaturation] = useState<number | null>(null);
+  const [loading, setLoading] = useState(false);
+  const loadingRef = useRef(false);
+
+  // 获取血氧饱和度数据 - 在页面聚焦、日期变化时触发
+  useFocusEffect(
+    useCallback(() => {
+      const loadOxygenSaturationData = async () => {
+        const dateToUse = selectedDate || new Date();
+
+        // 防止重复请求
+        if (loadingRef.current) return;
+
+        try {
+          loadingRef.current = true;
+          setLoading(true);
+
+          const options = {
+            startDate: dayjs(dateToUse).startOf('day').toDate().toISOString(),
+            endDate: dayjs(dateToUse).endOf('day').toDate().toISOString()
+          };
+
+          const data = await fetchOxygenSaturation(options);
+          setOxygenSaturation(data);
+        } catch (error) {
+          console.error('OxygenSaturationCard: 获取血氧饱和度数据失败:', error);
+          setOxygenSaturation(null);
+        } finally {
+          setLoading(false);
+          loadingRef.current = false;
+        }
+      };
+
+      loadOxygenSaturationData();
+    }, [selectedDate])
+  );
+
   return (
     <HealthDataCard
       title="血氧饱和度"
-      value={oxygenSaturation !== null && oxygenSaturation !== undefined ? oxygenSaturation.toFixed(1) : '--'}
+      value={loading ? '--' : (oxygenSaturation !== null && oxygenSaturation !== undefined ? oxygenSaturation.toFixed(1) : '--')}
       unit="%"
       style={style}
     />
   );
 };
 
-const styles = StyleSheet.create({
-  container: {
-    flex: 1,
-  },
-});
-
 export default OxygenSaturationCard;