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/stores/userStore.ts

@@ -254,18 +254,13 @@ export const useUserStore = create<UserState>((set, get) => {
     followUser: async (userId: string) => {
       const originalUsers = get().users;
       const originalUserCache = get().userCache;
-      
-      // 乐观更新 users
+
       set(state => ({
         users: state.users.map(u =>
           u.id === userId
             ? { ...u, isFollowing: true, followersCount: u.followers_count + 1 }
             : u
         ),
-      }));
-      
-      // 乐观更新 userCache
-      set(state => ({
         userCache: Object.fromEntries(
           Object.entries(state.userCache).map(([id, user]) => [
             id,
@@ -275,35 +270,25 @@ export const useUserStore = create<UserState>((set, get) => {
           ])
         )
       }));
-      
+
       try {
         await authService.followUser(userId);
       } catch (error) {
         console.error('关注用户失败:', error);
-        // 回滚
-        set({ 
-          users: originalUsers,
-          userCache: originalUserCache 
-        });
+        set({ users: originalUsers, userCache: originalUserCache });
       }
     },
     
-    // 取消关注 - authService 不管理状态，所以由 store 管理
     unfollowUser: async (userId: string) => {
       const originalUsers = get().users;
       const originalUserCache = get().userCache;
-      
-      // 乐观更新 users
+
       set(state => ({
         users: state.users.map(u =>
           u.id === userId
             ? { ...u, isFollowing: false, followersCount: Math.max(0, u.followers_count - 1) }
             : u
         ),
-      }));
-      
-      // 乐观更新 userCache
-      set(state => ({
         userCache: Object.fromEntries(
           Object.entries(state.userCache).map(([id, user]) => [
             id,
@@ -313,16 +298,12 @@ export const useUserStore = create<UserState>((set, get) => {
           ])
         )
       }));
-      
+
       try {
         await authService.unfollowUser(userId);
       } catch (error) {
         console.error('取消关注用户失败:', error);
-        // 回滚
-        set({ 
-          users: originalUsers,
-          userCache: originalUserCache 
-        });
+        set({ users: originalUsers, userCache: originalUserCache });
       }
     },