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/screens/message/GroupInfoScreen.tsx

@@ -1108,10 +1108,10 @@ function createGroupInfoStyles(colors: AppColors) {
     fontSize: fontSizes.xl,
     letterSpacing: 0.5,
   },
-  pageHeaderPlaceholder: {
-    width: 40,
-    height: 40,
-  },
+    pageHeaderPlaceholder: {
+      width: 40,
+      height: 40,
+    },
   scrollView: {
     flex: 1,
   },