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/data/mappers/PostMapper.ts

@@ -27,7 +27,12 @@ export class PostMapper {
       communityId: response.community_id,
       tags: [],
       createdAt: new Date(response.created_at || Date.now()),
-      updatedAt: new Date(response.updated_at || Date.now()),
+      // 空字符串/缺省时用 created_at，避免误用 Date.now() 导致全部显示「刚修改」
+      updatedAt: new Date(
+        response.updated_at ||
+          response.created_at ||
+          Date.now()
+      ),
     };
   }
 

src/data/repositories/PostRepository.ts

@@ -41,6 +41,7 @@ interface PostApiResponse {
   tags?: string[];
   created_at: string;
   updated_at: string;
+  content_edited_at?: string;
   author?: {
     id: number;
     username: string;
@@ -122,6 +123,7 @@ export class PostRepository implements IPostRepository {
       tags: model.tags || [],
       createdAt: model.createdAt.toISOString(),
       updatedAt: model.updatedAt.toISOString(),
+      contentEditedAt: response.content_edited_at,
       
       // snake_case 字段（向后兼容）
       likes_count: model.likeCount,
@@ -135,6 +137,7 @@ export class PostRepository implements IPostRepository {
       user_id: model.authorId,
       created_at: model.createdAt.toISOString(),
       updated_at: model.updatedAt.toISOString(),
+      content_edited_at: response.content_edited_at,
       community_id: model.communityId,
     };
   }