feat(auth): 预加载用户数据并优化登录状态同步

- 在启动屏预加载用户 token 与资料，避免首页白屏
- 新增 rehydrateUserSync 同步注入 Redux，减少异步等待
- 登录页兼容 ERR_REQUEST_CANCELED 取消场景
- 各页面统一依赖 isLoggedIn 判断，移除冗余控制台日志
- 步数卡片与详情页改为实时拉取健康数据，不再缓存至 Redux
- 后台任务注册移至顶层，防止重复定义
- 体重记录、HeaderBar 等 UI 细节样式微调

components/ui/HeaderBar.tsx

@@ -1,11 +1,11 @@
+import { Colors } from '@/constants/Colors';
+import { useColorScheme } from '@/hooks/useColorScheme';
 import { Ionicons } from '@expo/vector-icons';
+import { router } from 'expo-router';
 import React from 'react';
 import { StyleSheet, Text, TouchableOpacity, View } from 'react-native';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
 
-import { Colors } from '@/constants/Colors';
-import { useColorScheme } from '@/hooks/useColorScheme';
-
 export type HeaderBarProps = {
   title: string | React.ReactNode;
   onBack?: () => void;
@@ -76,23 +76,24 @@ export function HeaderBar({
         },
       ]}
     >
-      {onBack ? (
-        <TouchableOpacity
-          accessibilityRole="button"
-          onPress={onBack}
-          style={styles.backButton}
-          activeOpacity={0.7}
-        >
-          <Ionicons
-            name="chevron-back"
-            size={24}
-            color={backColor || theme.text}
-          />
-        </TouchableOpacity>
-      ) : (
-        <View style={{ width: 32 }} />
-      )}
-
+      <TouchableOpacity
+        accessibilityRole="button"
+        onPress={() => {
+          if (onBack) {
+            onBack();
+            return
+          }
+          router.back()
+        }}
+        style={styles.backButton}
+        activeOpacity={0.7}
+      >
+        <Ionicons
+          name="chevron-back"
+          size={24}
+          color={backColor || theme.text}
+        />
+      </TouchableOpacity>
       <View style={styles.titleContainer}>
         {typeof title === 'string' ? (
           <Text style={[