refactor(PostCard, ImageGrid, SmartImage): enhance post editing display and image handling

- Introduced a new method to determine the last edited time for posts, prioritizing content_edited_at for better accuracy in display.
- Updated PostCard and PostDetailScreen components to utilize the new editing display logic.
- Enhanced ImageGrid and SmartImage components to support additional preview URLs and improve image loading behavior, including lazy loading optimizations for web.
- Modified Post and PostDTO interfaces to include contentEditedAt for better tracking of post edits.

src/components/common/SmartImage.tsx

@@ -13,6 +13,7 @@ import {
   ActivityIndicator,
   Pressable,
   StyleProp,
+  Platform,
 } from 'react-native';
 import { Image as ExpoImage } from 'expo-image';
 import { MaterialCommunityIcons } from '@expo/vector-icons';
@@ -61,6 +62,8 @@ export interface SmartImageProps {
   usePreview?: boolean;
   /** 是否懒加载 */
   lazyLoad?: boolean;
+  /** Web 端 IntersectionObserver rootMargin，略提前加载进入视口附近的图 */
+  lazyRootMargin?: string;
   /** 缓存策略 */
   cachePolicy?: 'memory' | 'disk' | 'memory-disk' | 'none';
 }
@@ -85,11 +88,13 @@ export const SmartImage: React.FC<SmartImageProps> = ({
   previewUrl,
   usePreview = false,
   lazyLoad = false,
+  lazyRootMargin = '160px',
   cachePolicy = 'memory-disk',
 }) => {
   const [loadState, setLoadState] = useState<ImageLoadState>('loading');
-  const [isVisible, setIsVisible] = useState(!lazyLoad);
+  const [isVisible, setIsVisible] = useState(() => !lazyLoad || Platform.OS !== 'web');
   const [shouldLoadOriginal, setShouldLoadOriginal] = useState(false);
+  const lazyTargetRef = useRef<View>(null);
 
   // 解析图片源 - 支持 uri 或 url 字段
   const imageUri = typeof source === 'string'
@@ -99,6 +104,39 @@ export const SmartImage: React.FC<SmartImageProps> = ({
   // 解析预览图 URL
   const previewUri = typeof previewUrl === 'string' ? previewUrl : '';
 
+  useEffect(() => {
+    setShouldLoadOriginal(false);
+    setLoadState('loading');
+  }, [imageUri]);
+
+  useEffect(() => {
+    if (!lazyLoad) {
+      setIsVisible(true);
+      return;
+    }
+    if (Platform.OS !== 'web') {
+      setIsVisible(true);
+      return;
+    }
+    setIsVisible(false);
+    const node = lazyTargetRef.current as unknown as Element | null;
+    if (!node || typeof IntersectionObserver === 'undefined') {
+      setIsVisible(true);
+      return;
+    }
+    const observer = new IntersectionObserver(
+      entries => {
+        if (entries.some(e => e.isIntersecting)) {
+          setIsVisible(true);
+          observer.disconnect();
+        }
+      },
+      { rootMargin: lazyRootMargin }
+    );
+    observer.observe(node);
+    return () => observer.disconnect();
+  }, [lazyLoad, lazyRootMargin, imageUri]);
+
   // 智能选择图片 URL
   const getImageUrl = useCallback((): string => {
     // 如果应该加载原图（预览图已加载完成或没有预览图）
@@ -200,10 +238,12 @@ export const SmartImage: React.FC<SmartImageProps> = ({
     );
   }
 
-  // 如果是懒加载且不可见，显示占位
+  // 如果是懒加载且不可见，显示占位（Web 上由 IntersectionObserver 驱动进入视口后再加载）
   if (lazyLoad && !isVisible) {
     return (
       <View
+        ref={Platform.OS === 'web' ? lazyTargetRef : undefined}
+        collapsable={false}
         style={[containerStyle, style as ViewStyle, { backgroundColor: '#F5F5F5' }]}
         testID={testID}
       />