refactor(ui): implement custom header system and unify screen layouts

Refactor the navigation and header strategy by replacing native stack headers with a custom `SimpleHeader` component across most profile and detail screens. This provides a more consistent UI/UX and better control over layout behavior.

- Implement `SimpleHeader` component in `src/components/common`.
- Disable native header rendering in `app/(app)/(tabs)/profile/_layout.tsx` and `app/_layout.tsx`.
- Update profile sub-screens to use `SimpleHeader` and `StatusBar` from `expo-status-bar`.
- Refactor `PostDetailScreen` to use a custom header implementation for better integration with the post author information.
- Update `UserScreen` to wrap content in `SafeAreaView` with the new header.
- Adjust `AppBackButton` to support transparent backgrounds.

src/screens/home/PostDetailScreen.tsx

@@ -23,8 +23,9 @@ import {
   Dimensions,
 } from 'react-native';
 import { FlashList, ListRenderItem, FlashListRef } from '@shopify/flash-list';
-import { useSafeAreaInsets } from 'react-native-safe-area-context';
+import { SafeAreaView, useSafeAreaInsets } from 'react-native-safe-area-context';
 import { useNavigation, useRouter, useLocalSearchParams } from 'expo-router';
+import { StatusBar } from 'expo-status-bar';
 import { MaterialCommunityIcons } from '@expo/vector-icons';
 import * as ImagePicker from 'expo-image-picker';
 import {
@@ -131,6 +132,7 @@ export const PostDetailScreen: React.FC = () => {
     postId?: string;
     scrollToComments?: string;
   }>();
+
   const postId = postIdParam || '';
   const shouldScrollToComments = scrollParam === '1' || scrollParam === 'true';
   
@@ -367,58 +369,43 @@ export const PostDetailScreen: React.FC = () => {
     }
   }, [shouldScrollToComments, isPostInitialLoading, comments?.length]);
 
-  // 动态设置导航头部
-  useEffect(() => {
-    if (!post?.author) return;
-    
-    const author = post.author;
-    const handleBackPress = () => {
-      if (router.canGoBack()) {
-        router.back();
-        return;
-      }
-      router.replace(hrefs.hrefHome());
-    };
-    
-    navigation.setOptions({
-      // 与页面容器 background.default 一致，并去掉原生 header 底部分隔阴影，避免「一条线」
-      headerStyle: { backgroundColor: colors.background.default },
-      headerShadowVisible: false,
-      headerBackVisible: false,
-      headerTitleAlign: 'left',
-      headerLeft: () => (
-        <AppBackButton onPress={handleBackPress} style={styles.headerBackButton} />
-      ),
-      headerTitle: () => (
+  const handleBackPress = useCallback(() => {
+    if (router.canGoBack()) {
+      router.back();
+      return;
+    }
+    router.replace(hrefs.hrefHome());
+  }, [router]);
+
+  const renderCustomHeader = () => (
+    <View style={styles.customHeader}>
+      <AppBackButton onPress={handleBackPress} style={styles.headerBackButton} />
+      {post?.author ? (
         <View style={styles.headerContainer}>
           <TouchableOpacity
-            onPress={() => handleUserPress(author.id)}
+            onPress={() => handleUserPress(post.author!.id)}
             style={styles.headerAvatarWrapper}
           >
-            <Avatar
-              source={author.avatar}
-              size={32}
-              name={author.nickname}
-            />
+            <Avatar source={post.author.avatar} size={32} name={post.author.nickname} />
           </TouchableOpacity>
           <View style={styles.headerUserInfo}>
-            <TouchableOpacity onPress={() => handleUserPress(author.id)}>
+            <TouchableOpacity onPress={() => handleUserPress(post.author!.id)}>
               <Text style={styles.headerNickname} numberOfLines={1}>
-                {author.nickname && author.nickname.length > 10
-                  ? `${author.nickname.slice(0, 10)}...`
-                  : author.nickname}
+                {post.author.nickname && post.author.nickname.length > 10
+                  ? `${post.author.nickname.slice(0, 10)}...`
+                  : post.author.nickname}
               </Text>
             </TouchableOpacity>
           </View>
         </View>
-      ),
-      headerRight: () => (
-        <View style={styles.headerRightContainer}>
-          {renderFollowButton()}
-        </View>
-      ),
-    });
-  }, [post?.author, isFollowing, isFollowingMe, isFollowLoading, navigation, colors.background.default, styles]);
+      ) : (
+        <View style={styles.headerPlaceholder} />
+      )}
+      <View style={styles.headerRightContainer}>
+        {renderFollowButton()}
+      </View>
+    </View>
+  );
 
   // 监听键盘事件
   useEffect(() => {
@@ -1076,12 +1063,15 @@ export const PostDetailScreen: React.FC = () => {
     }
   };
 
-  // 渲染关注按钮
-  const renderFollowButton = () => {
-    if (!post?.author?.id || currentUser?.id === post.author.id) return null;
-    
+  // 渲染关注按钮（始终返回同尺寸占位，避免 header 右侧宽度跳动）
+  const renderFollowButton = useCallback(() => {
+    const shouldShow = post?.author?.id && currentUser?.id !== post.author.id;
+    if (!shouldShow) {
+      return <View style={styles.followButtonPlaceholder} />;
+    }
+
     const config = getFollowButtonConfig();
-    
+
     return (
       <TouchableOpacity
         style={[
@@ -1107,7 +1097,7 @@ export const PostDetailScreen: React.FC = () => {
         </Text>
       </TouchableOpacity>
     );
-  };
+  }, [post?.author?.id, currentUser?.id, isFollowing, isFollowingMe, isFollowLoading, styles]);
 
   // 使用 useMemo 缓存图片数据，避免输入时重新创建数组导致图片重新加载
   const postImages = useMemo(() => {
@@ -1712,7 +1702,9 @@ export const PostDetailScreen: React.FC = () => {
   // 桌面端双栏布局
   if (useDualColumnLayout) {
     return (
-      <View style={styles.container}>
+      <SafeAreaView style={styles.container} edges={['top']}>
+        <StatusBar style="auto" />
+        {renderCustomHeader()}
         <AdaptiveLayout
           sidebar={renderSidebar()}
           sidebarWidth={sidebarWidth}
@@ -1780,17 +1772,19 @@ export const PostDetailScreen: React.FC = () => {
           onClose={() => setShowImageModal(false)}
           enableSave
         />
-      </View>
+      </SafeAreaView>
     );
   }
 
   // 移动端单栏布局
   return (
-    <View style={styles.container}>
+    <SafeAreaView style={styles.container} edges={['top']}>
+      <StatusBar style="auto" />
+      {renderCustomHeader()}
       <KeyboardAvoidingView
         style={styles.flex}
         behavior={Platform.OS === 'ios' ? 'padding' : undefined}
-        keyboardVerticalOffset={88}
+        keyboardVerticalOffset={Platform.OS === 'ios' ? 0 : undefined}
       >
         <FlashList
           ref={flatListRef}
@@ -1896,7 +1890,7 @@ export const PostDetailScreen: React.FC = () => {
           }
         }}
       />
-    </View>
+    </SafeAreaView>
   );
 };
 
@@ -1909,6 +1903,16 @@ function createPostDetailStyles(colors: AppColors) {
     flex: 1,
     backgroundColor: colors.background.default,
   },
+  customHeader: {
+    flexDirection: 'row',
+    alignItems: 'center',
+    backgroundColor: colors.background.default,
+    height: 52,
+    paddingRight: spacing.sm,
+  },
+  headerPlaceholder: {
+    flex: 1,
+  },
   // Header 样式
   headerContainer: {
     flexDirection: 'row',
@@ -1932,10 +1936,12 @@ function createPostDetailStyles(colors: AppColors) {
     flexDirection: 'row',
     alignItems: 'center',
     marginRight: spacing.sm,
+    backgroundColor: 'transparent',
   },
   headerBackButton: {
     marginLeft: 0,
     marginRight: 0,
+    backgroundColor: 'transparent',
   },
   // 帖子容器
   postContainer: {
@@ -1950,6 +1956,7 @@ function createPostDetailStyles(colors: AppColors) {
     minWidth: 64,
     alignItems: 'center',
     justifyContent: 'center',
+    backgroundColor: 'transparent',
   },
   followButtonPrimary: {
     backgroundColor: colors.primary.main,
@@ -1967,6 +1974,12 @@ function createPostDetailStyles(colors: AppColors) {
   followButtonLoading: {
     opacity: 0.7,
   },
+  followButtonPlaceholder: {
+    minWidth: 64,
+    paddingHorizontal: spacing.md,
+    paddingVertical: 4,
+    backgroundColor: 'transparent',
+  },
   followButtonText: {
     fontSize: fontSizes.sm,
     fontWeight: '600',