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/screens/create/CreatePostScreen.tsx

@@ -795,6 +795,7 @@ export const CreatePostScreen: React.FC<CreatePostScreenProps> = (props) => {
         contentContainerStyle={styles.scrollContent}
         showsVerticalScrollIndicator={false}
         keyboardShouldPersistTaps="handled"
+        nestedScrollEnabled
       >
         {/* 内容输入区 */}
         {renderContentSection()}