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

utils/health.ts

@@ -216,8 +216,6 @@ export type TodayHealthData = {
   exerciseMinutesGoal: number;
   standHours: number;
   standHoursGoal: number;
-  // 新增血氧饱和度和心率数据
-  oxygenSaturation: number | null;
   heartRate: number | null;
 };
 
@@ -529,7 +527,7 @@ async function fetchActivitySummary(options: HealthDataOptions): Promise<HealthA
   }
 }
 
-async function fetchOxygenSaturation(options: HealthDataOptions): Promise<number | null> {
+export async function fetchOxygenSaturation(options: HealthDataOptions): Promise<number | null> {
   try {
     const result = await HealthKitManager.getOxygenSaturationSamples(options);
 
@@ -618,7 +616,6 @@ function getDefaultHealthData(): TodayHealthData {
     exerciseMinutesGoal: 30,
     standHours: 0,
     standHoursGoal: 12,
-    oxygenSaturation: null,
     heartRate: null,
   };
 }
@@ -636,14 +633,12 @@ export async function fetchHealthDataForDate(date: Date): Promise<TodayHealthDat
       basalEnergyBurned,
       hrv,
       activitySummary,
-      oxygenSaturation,
       heartRate
     ] = await Promise.all([
       fetchActiveEnergyBurned(options),
       fetchBasalEnergyBurned(options),
       fetchHeartRateVariability(options),
       fetchActivitySummary(options),
-      fetchOxygenSaturation(options),
       fetchHeartRate(options)
     ]);
 
@@ -657,7 +652,6 @@ export async function fetchHealthDataForDate(date: Date): Promise<TodayHealthDat
       exerciseMinutesGoal: Math.round(activitySummary?.appleExerciseTimeGoal || 30),
       standHours: Math.round(activitySummary?.appleStandHours || 0),
       standHoursGoal: Math.round(activitySummary?.appleStandHoursGoal || 12),
-      oxygenSaturation,
       heartRate
     };
   } catch (error) {