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

app/(tabs)/goals.tsx

@@ -109,6 +109,8 @@ export default function GoalsScreen() {
   const onRefresh = async () => {
     setRefreshing(true);
     try {
+      if (!isLoggedIn) return
+
       await loadTasks();
     } finally {
       setRefreshing(false);
@@ -117,6 +119,8 @@ export default function GoalsScreen() {
 
   // 加载更多任务
   const handleLoadMoreTasks = async () => {
+    if (!isLoggedIn) return
+
     if (tasksPagination.hasMore && !tasksLoading) {
       try {
         await dispatch(loadMoreTasks()).unwrap();
@@ -319,6 +323,61 @@ export default function GoalsScreen() {
 
   // 渲染空状态
   const renderEmptyState = () => {
+    // 未登录状态下的引导
+    if (!isLoggedIn) {
+      return (
+        <View style={styles.emptyStateLogin}>
+          <LinearGradient
+            colors={['#F0F9FF', '#FEFEFE', '#F0F9FF']}
+            style={styles.emptyStateLoginBackground}
+            start={{ x: 0, y: 0 }}
+            end={{ x: 1, y: 1 }}
+          />
+
+          <View style={styles.emptyStateLoginContent}>
+            {/* 清新的图标设计 */}
+            <View style={styles.emptyStateLoginIconContainer}>
+              <LinearGradient
+                colors={[colorTokens.primary, '#9B8AFB']}
+                style={styles.emptyStateLoginIconGradient}
+                start={{ x: 0, y: 0 }}
+                end={{ x: 1, y: 1 }}
+              >
+                <MaterialIcons name="person-outline" size={32} color="#FFFFFF" />
+              </LinearGradient>
+            </View>
+
+            {/* 主标题 */}
+            <Text style={[styles.emptyStateLoginTitle, { color: colorTokens.text }]}>
+              开启您的健康之旅
+            </Text>
+
+            {/* 副标题 */}
+            <Text style={[styles.emptyStateLoginSubtitle, { color: colorTokens.textSecondary }]}>
+              登录后即可创建个人目标，让我们一起建立健康的生活习惯
+            </Text>
+
+            {/* 登录按钮 */}
+            <TouchableOpacity
+              style={[styles.emptyStateLoginButton, { backgroundColor: colorTokens.primary }]}
+              onPress={() => pushIfAuthedElseLogin('/goals')}
+            >
+              <LinearGradient
+                colors={[colorTokens.primary, '#9B8AFB']}
+                style={styles.emptyStateLoginButtonGradient}
+                start={{ x: 0, y: 0 }}
+                end={{ x: 1, y: 1 }}
+              >
+                <Text style={styles.emptyStateLoginButtonText}>立即登录</Text>
+                <MaterialIcons name="arrow-forward" size={18} color="#FFFFFF" />
+              </LinearGradient>
+            </TouchableOpacity>
+          </View>
+        </View>
+      );
+    }
+
+    // 已登录但无任务的状态
     let title = '暂无任务';
     let subtitle = '创建目标后，系统会自动生成相应的任务';
 
@@ -710,6 +769,80 @@ const styles = StyleSheet.create({
     textAlign: 'center',
     lineHeight: 20,
   },
+  // 未登录空状态样式
+  emptyStateLogin: {
+    flex: 1,
+    alignItems: 'center',
+    justifyContent: 'center',
+    paddingHorizontal: 24,
+    paddingVertical: 80,
+    position: 'relative',
+  },
+  emptyStateLoginBackground: {
+    position: 'absolute',
+    left: 0,
+    right: 0,
+    top: 0,
+    bottom: 0,
+    borderRadius: 24,
+  },
+  emptyStateLoginContent: {
+    alignItems: 'center',
+    justifyContent: 'center',
+    zIndex: 1,
+  },
+  emptyStateLoginIconContainer: {
+    marginBottom: 24,
+    shadowColor: '#7A5AF8',
+    shadowOffset: { width: 0, height: 8 },
+    shadowOpacity: 0.15,
+    shadowRadius: 16,
+    elevation: 8,
+  },
+  emptyStateLoginIconGradient: {
+    width: 80,
+    height: 80,
+    borderRadius: 40,
+    alignItems: 'center',
+    justifyContent: 'center',
+  },
+  emptyStateLoginTitle: {
+    fontSize: 24,
+    fontWeight: '700',
+    marginBottom: 12,
+    textAlign: 'center',
+    letterSpacing: -0.5,
+  },
+  emptyStateLoginSubtitle: {
+    fontSize: 16,
+    lineHeight: 24,
+    textAlign: 'center',
+    marginBottom: 32,
+    paddingHorizontal: 8,
+  },
+  emptyStateLoginButton: {
+    borderRadius: 28,
+    shadowColor: '#7A5AF8',
+    shadowOffset: { width: 0, height: 4 },
+    shadowOpacity: 0.2,
+    shadowRadius: 12,
+    elevation: 6,
+  },
+  emptyStateLoginButtonGradient: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    justifyContent: 'center',
+    paddingHorizontal: 32,
+    paddingVertical: 16,
+    borderRadius: 28,
+    gap: 8,
+  },
+  emptyStateLoginButtonText: {
+    color: '#FFFFFF',
+    fontSize: 17,
+    fontWeight: '600',
+    letterSpacing: -0.2,
+  },
   loadMoreContainer: {
     alignItems: 'center',
     paddingVertical: 20,