feat: 添加用户登录和法律协议页面

- 新增登录页面，支持 Apple 登录和游客登录功能
- 添加用户协议和隐私政策页面，用户需同意后才能登录
- 更新首页逻辑，首次进入时自动跳转到登录页面
- 修改个人信息页面，移除单位选择功能，统一使用 kg 和 cm
- 更新依赖，添加 expo-apple-authentication 库以支持 Apple 登录
- 更新布局以适应新功能的展示和交互

app/(tabs)/explore.tsx

@@ -187,7 +187,13 @@ export default function ExploreScreen() {
                 ) : (
                   <Text style={styles.stepsValue}>——/2000</Text>
                 )}
-                <ProgressBar progress={Math.min(1, Math.max(0, (stepCount ?? 0) / 2000))} height={12} trackColor="#FFEBCB" fillColor="#FFC365" />
+                <ProgressBar
+                  progress={Math.min(1, Math.max(0, (stepCount ?? 0) / 2000))}
+                  height={18}
+                  trackColor="#FFEBCB"
+                  fillColor="#FFC365"
+                  showLabel={false}
+                />
               </View>
             </View>
           </View>

app/(tabs)/index.tsx

@@ -5,7 +5,7 @@ import { ThemedView } from '@/components/ThemedView';
 import { WorkoutCard } from '@/components/WorkoutCard';
 import { getChineseGreeting } from '@/utils/date';
 import { useRouter } from 'expo-router';
-import React from 'react';
+import React, { useEffect, useRef } from 'react';
 import { SafeAreaView, ScrollView, StyleSheet, View } from 'react-native';
 
 const workoutData = [
@@ -24,6 +24,15 @@ const workoutData = [
 
 export default function HomeScreen() {
   const router = useRouter();
+  const hasOpenedLoginRef = useRef(false);
+
+  useEffect(() => {
+    // 仅在本次会话首次进入首页时打开登录页，可返回关闭
+    if (!hasOpenedLoginRef.current) {
+      hasOpenedLoginRef.current = true;
+      router.push('/auth/login');
+    }
+  }, [router]);
   return (
     <SafeAreaView style={styles.safeArea}>
       <ThemedView style={styles.container}>

app/(tabs)/personal.tsx

@@ -31,8 +31,6 @@ export default function PersonalScreen() {
   const colorScheme = useColorScheme();
   const colors = Colors[colorScheme ?? 'light'];
 
-  type WeightUnit = 'kg' | 'lb';
-  type HeightUnit = 'cm' | 'ft';
   type UserProfile = {
     fullName?: string;
     email?: string;
@@ -40,7 +38,7 @@ export default function PersonalScreen() {
     age?: string;
     weightKg?: number;
     heightCm?: number;
-    unitPref?: { weight: WeightUnit; height: HeightUnit };
+    avatarUri?: string | null;
   };
 
   const [profile, setProfile] = useState<UserProfile>({});
@@ -78,16 +76,12 @@ export default function PersonalScreen() {
 
   const formatHeight = () => {
     if (profile.heightCm == null) return '--';
-    const unit = profile.unitPref?.height ?? 'cm';
-    if (unit === 'cm') return `${Math.round(profile.heightCm)}cm`;
-    return `${round(profile.heightCm / 30.48, 1)}ft`;
+    return `${Math.round(profile.heightCm)}cm`;
   };
 
   const formatWeight = () => {
     if (profile.weightKg == null) return '--';
-    const unit = profile.unitPref?.weight ?? 'kg';
-    if (unit === 'kg') return `${round(profile.weightKg, 1)}kg`;
-    return `${round(profile.weightKg * 2.2046226218, 1)}lb`;
+    return `${round(profile.weightKg, 1)}kg`;
   };
 
   const formatAge = () => (profile.age ? `${profile.age}岁` : '--');