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/GroupInfoScreen.tsx

@@ -46,6 +46,7 @@ import {
   JoinType,
 } from '../../types/dto';
 import { User } from '../../types';
+import { blurActiveElement } from '../../infrastructure/platform';
 import { firstRouteParam } from '../../navigation/paramUtils';
 import * as hrefs from '../../navigation/hrefs';
 import { messageManager } from '../../stores/messageManager';
@@ -119,9 +120,8 @@ const GroupInfoScreen: React.FC = () => {
   const [inviting, setInviting] = useState(false);
 
   useEffect(() => {
-    if ((editModalVisible || announcementModalVisible || transferModalVisible || joinTypeModalVisible || inviteModalVisible) && Platform.OS === 'web') {
-      const active = (globalThis as any)?.document?.activeElement as { blur?: () => void } | undefined;
-      active?.blur?.();
+    if (editModalVisible || announcementModalVisible || transferModalVisible || joinTypeModalVisible || inviteModalVisible) {
+      blurActiveElement();
     }
   }, [editModalVisible, announcementModalVisible, transferModalVisible, joinTypeModalVisible, inviteModalVisible]);