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/EmojiPanel.tsx

@@ -15,15 +15,10 @@ import { useResponsive, useBreakpointGTE } from '../../../../hooks/useResponsive
 import { EMOJIS } from './constants';
 import { CustomSticker, getCustomStickers, batchDeleteStickers, addStickerFromUrl } from '../../../../services/stickerService';
 import { useAppColors, spacing } from '../../../../theme';
+import { blurActiveElement } from '../../../../infrastructure/platform';
 
 const { height: SCREEN_HEIGHT } = Dimensions.get('window');
 
-const blurActiveElementOnWeb = () => {
-  if (Platform.OS !== 'web') return;
-  const active = (globalThis as any)?.document?.activeElement as { blur?: () => void } | undefined;
-  active?.blur?.();
-};
-
 // 表情尺寸配置 - 固定宽度 40px，使用 flex 布局
 const EMOJI_SIZES = {
   mobile: { size: 24, itemWidth: 40, itemHeight: 40 },
@@ -182,7 +177,7 @@ export const EmojiPanel: React.FC<EmojiPanelProps> = ({
 
   // 打开管理界面
   const handleOpenManage = () => {
-    blurActiveElementOnWeb();
+    blurActiveElement();
     setShowManageModal(true);
     setManageMode(false);
     setSelectedStickers(new Set());