refactor: 移除不必要的布局效果，简化任务列表屏幕的代码结构，同时添加下拉刷新功能的支持

src/screens/TaskListScreen.tsx

@@ -1,14 +1,7 @@
-import React, { useLayoutEffect, useState, useCallback } from 'react';
-import {
-  View,
-  StyleSheet,
-  FlatList,
-  TouchableOpacity,
-  ActivityIndicator,
-} from 'react-native';
+import React, { useState, useCallback } from 'react';
+import { View, StyleSheet, FlatList } from 'react-native';
 import { useNavigation } from '@react-navigation/native';
 import { StackNavigationProp } from '@react-navigation/stack';
-import MaterialIcons from 'react-native-vector-icons/MaterialIcons';
 import { useTasks } from '../context/TasksContext';
 import TaskCard from '../components/TaskCard';
 
@@ -38,20 +31,6 @@ export default function TaskListScreen() {
     }
   }, [refreshTasks]);
 
-  useLayoutEffect(() => {
-    navigation.setOptions({
-      headerRight: () => (
-        <TouchableOpacity onPress={handleRefresh} style={{ marginRight: 15 }}>
-          {isRefreshing ? (
-            <ActivityIndicator size="small" color="#ffffff" />
-          ) : (
-            <MaterialIcons name="refresh" size={24} color="#ffffff" />
-          )}
-        </TouchableOpacity>
-      ),
-    });
-  }, [navigation, isRefreshing, handleRefresh]);
-
   const handlePressTask = (id: string) => {
     navigation.navigate('TaskEdit', { taskId: id });
   };
@@ -67,6 +46,8 @@ export default function TaskListScreen() {
         renderItem={renderItem}
         keyExtractor={item => item.id}
         ItemSeparatorComponent={() => <View style={styles.separator} />}
+        refreshing={isRefreshing}
+        onRefresh={handleRefresh}
       />
     </View>
   );