feat(post): add post reference functionality with inline cards and suggestion search

Add support for referencing/quoting other posts within post content. Includes:
- New `post_ref` segment type with `PostRefSegmentData` interface for post references
- New `PostRefCard` component to display referenced posts inline
- Post suggestion search triggered by `#` in `PostMentionInput`
- Updated `PostContentRenderer` to render post reference segments
- Add `suggestPosts` and `recordRefClick` API methods in postService

Additional improvements:
- Add image gallery preview for user profile covers and avatars
- Make text selectable across CommentItem, PostContentRenderer, and PostDetailScreen
- Migrate FlatList to FlashList in PostDetailScreen and UserProfileScreen
- Add nestedScrollEnabled to CreatePostScreen
- Add clickable member avatars in GroupMembersScreen

src/services/post/postService.ts

@@ -420,6 +420,23 @@ class PostService {
       };
     }
   }
+
+  async suggestPosts(keyword: string, limit = 10): Promise<Array<{ id: string; title: string; channel?: string }>> {
+    try {
+      const response = await api.get<any>('/posts/suggest', { q: keyword, limit });
+      return response.data ?? [];
+    } catch {
+      return [];
+    }
+  }
+
+  async recordRefClick(sourcePostId: string, targetPostId: string): Promise<void> {
+    try {
+      await api.post(`/posts/${sourcePostId}/ref-click`, { target_post_id: targetPostId });
+    } catch {
+      // ignore
+    }
+  }
 }
 
 // 导出帖子服务实例