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/components/common/AdaptiveLayout.tsx

@@ -22,6 +22,7 @@ import {
   useBreakpointGTE,
   FineBreakpointKey,
 } from '../../hooks/useResponsive';
+import { blurActiveElement } from '../../infrastructure/platform';
 
 export interface AdaptiveLayoutProps {
   /** 主内容区 */
@@ -160,9 +161,8 @@ export function AdaptiveLayout({
   // 抽屉动画
   useEffect(() => {
     if (isDrawerOpen) {
-      if (Platform.OS === 'web') {
-        const active = (globalThis as any)?.document?.activeElement as { blur?: () => void } | undefined;
-        active?.blur?.();
+      if (isDrawerOpen) {
+        blurActiveElement();
       }
       Animated.parallel([
         Animated.timing(slideAnim, {