feat(auth): 为登录页面添加Liquid Glass效果并更新文案

- 使用expo-glass-effect为返回按钮添加毛玻璃效果
- 添加兼容性处理，在不支持时使用fallback样式
- 更新副标题文案为"健康生活，自律让我更自由"
- 优化返回按钮尺寸和圆角样式

app/auth/login.tsx

@@ -1,5 +1,6 @@
 import { Ionicons } from '@expo/vector-icons';
 import * as AppleAuthentication from 'expo-apple-authentication';
+import { GlassView, isLiquidGlassAvailable } from 'expo-glass-effect';
 import { LinearGradient } from 'expo-linear-gradient';
 import { useLocalSearchParams, useRouter } from 'expo-router';
 import React, { useCallback, useEffect, useMemo, useRef, useState } from 'react';
@@ -219,9 +220,22 @@ export default function LoginScreen() {
         </View>
         {/* 自定义头部，与其它页面风格一致 */}
         <View style={styles.header}>
-          <TouchableOpacity accessibilityRole="button" onPress={() => router.back()} style={styles.backButton}>
+          {isLiquidGlassAvailable() ? (
+            <TouchableOpacity accessibilityRole="button" onPress={() => router.back()} activeOpacity={0.7}>
+              <GlassView
+                style={styles.backButton}
+                glassEffectStyle="clear"
+                tintColor="rgba(255, 255, 255, 0.2)"
+                isInteractive={true}
+              >
+                <Ionicons name="chevron-back" size={24} color={scheme === 'dark' ? '#ECEDEE' : '#192126'} />
+              </GlassView>
+            </TouchableOpacity>
+          ) : (
+            <TouchableOpacity accessibilityRole="button" onPress={() => router.back()} style={[styles.backButton, styles.fallbackBackground]} activeOpacity={0.7}>
               <Ionicons name="chevron-back" size={24} color={scheme === 'dark' ? '#ECEDEE' : '#192126'} />
             </TouchableOpacity>
+          )}
           <Text style={[styles.headerTitle, { color: color.text }]}>登录</Text>
           <View style={{ width: 32 }} />
         </View>
@@ -229,7 +243,7 @@ export default function LoginScreen() {
         <ScrollView contentContainerStyle={styles.content} showsVerticalScrollIndicator={false}>
           <View style={styles.headerWrap}>
             <ThemedText style={[styles.title, { color: color.text }]}>Out Live</ThemedText>
-            <ThemedText style={[styles.subtitle, { color: color.textMuted }]}>欢迎登录Out Live</ThemedText>
+            <ThemedText style={[styles.subtitle, { color: color.textMuted }]}>健康生活，自律让我更自由</ThemedText>
           </View>
 
           {/* Apple 登录 */}
@@ -296,7 +310,17 @@ const styles = StyleSheet.create({
     paddingTop: 4,
     paddingBottom: 8,
   },
-  backButton: { width: 32, height: 32, alignItems: 'center', justifyContent: 'center' },
+  backButton: {
+    width: 38,
+    height: 38,
+    alignItems: 'center',
+    justifyContent: 'center',
+    borderRadius: 38,
+    overflow: 'hidden',
+  },
+  fallbackBackground: {
+    backgroundColor: 'rgba(255, 255, 255, 0.5)',
+  },
   headerTitle: { fontSize: 18, fontWeight: '700' },
   headerWrap: {
     marginBottom: 36,