feat(ui): unify design system to Twitter/X style across screens and improve message handling

Redesign multiple screens and components from card-based responsive design to Twitter/X flat design:
- UserProfileHeader: adopt Twitter/X style with larger icons, simplified buttons, and block functionality
- AppBackButton: update to chevron-left icon with larger size, remove background styling
- Update SettingsScreen, EditProfileScreen, and UserProfileScreen with flat layout approach
- ConversationListRow: convert from bordered cards to flat list rows with updated typography

Improve message system with WebSocket notification handling:
- Add real-time system unread count updates via WebSocket
- Track lastSystemMessageAt for accurate system message timestamps
- Add notification deduplication and read-status filtering
- Combine system and conversation unread counts in background sync
- Clear system notifications from notification center on mark as read

src/stores/message/services/MessageSyncService.ts

@@ -376,6 +376,18 @@ export class MessageSyncService implements IMessageSyncService {
 
       store.setUnreadCount(totalUnread, systemUnread);
 
+      // 获取最后一条系统通知的时间
+      if (systemUnread > 0) {
+        try {
+          const latestSystemMsg = await messageService.getSystemMessagesCursor({ cursor: '', page_size: 1 });
+          if (latestSystemMsg?.list?.[0]?.created_at) {
+            store.setLastSystemMessageAt(latestSystemMsg.list[0].created_at);
+          }
+        } catch {
+          // 获取最后系统通知时间失败，不影响主流程
+        }
+      }
+
       // 服务端汇总未读为 0 时，清掉内存中残留的红点
       if (totalUnread === 0) {
         const currentConversations = store.getState().conversations;