refactor(platform): extract blurActiveElement to infrastructure module

- Centralize duplicated Platform.OS === 'web' blur logic across 16 components
- Add blurActiveElement utility to src/infrastructure/platform module
- Optimize MessageBubble and ImageSegment with React.memo custom comparators
- Add useMemo for computed values in MessageSegmentsRenderer
- Update DTO types with is_system_notice and notice_content fields
- Fix keyboard dismissal order in useChatScreen handleDismiss
- Simplify userStore follow/unfollow state updates
- Remove unnecessary TypeScript type assertions throughout codebase

src/screens/message/components/ChatScreen/MessageBubble.tsx

@@ -31,7 +31,7 @@ const MAX_WIDTH_RATIO = {
   desktop: 0.55,
 };
 
-export const MessageBubble: React.FC<MessageBubbleProps> = ({
+const MessageBubbleInner: React.FC<MessageBubbleProps> = ({
   message,
   index,
   currentUserId,
@@ -481,11 +481,37 @@ const segmentStyles = StyleSheet.create({
     minWidth: 120,
   },
   pureImageBubble: {
-    // 纯图片消息：去除内边距，让图片紧贴气泡边缘
     paddingHorizontal: 0,
     paddingVertical: 0,
     overflow: 'hidden',
+    backgroundColor: 'transparent',
   },
 });
 
+export const MessageBubble = React.memo(MessageBubbleInner, (prev, next) => {
+  if (prev.message.id !== next.message.id) return false;
+  if (prev.message.status !== next.message.status) return false;
+  if (prev.message.segments !== next.message.segments) return false;
+  if (prev.message.sender_id !== next.message.sender_id) return false;
+  if (prev.message.is_system_notice !== next.message.is_system_notice) return false;
+  if (prev.message.category !== next.message.category) return false;
+  if (prev.message.seq !== next.message.seq) return false;
+  if (prev.message.sender !== next.message.sender) return false;
+  if (prev.message.notice_content !== next.message.notice_content) return false;
+  if (prev.index !== next.index) return false;
+  if (prev.currentUserId !== next.currentUserId) return false;
+  if (prev.otherUserLastReadSeq !== next.otherUserLastReadSeq) return false;
+  if (prev.selectedMessageId !== next.selectedMessageId) return false;
+  if (prev.isGroupChat !== next.isGroupChat) return false;
+  if (prev.groupMembers !== next.groupMembers) return false;
+  if (prev.currentUser !== next.currentUser) return false;
+  if (prev.otherUser !== next.otherUser) return false;
+  if (prev.messageMap !== next.messageMap) return false;
+  if (prev.onLongPress !== next.onLongPress) return false;
+  if (prev.onImagePress !== next.onImagePress) return false;
+  if (prev.onReplyPress !== next.onReplyPress) return false;
+  if (prev.shouldShowTime !== next.shouldShowTime) return false;
+  return true;
+});
+
 export default MessageBubble;