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/components/ConversationListRow.tsx

@@ -157,32 +157,27 @@ function createConversationRowStyles(colors: AppColors) {
       alignItems: 'center',
       paddingHorizontal: spacing.md,
       paddingVertical: 14,
-      backgroundColor: colors.background.paper,
-      marginHorizontal: spacing.md,
-      marginTop: spacing.sm,
-      borderRadius: borderRadius.lg,
-      borderWidth: 0.5,
-      borderColor: colors.divider + '40',
+      backgroundColor: colors.background.default,
+      borderBottomWidth: StyleSheet.hairlineWidth,
+      borderBottomColor: colors.chat.borderLight,
     },
     conversationItemSelected: {
-      backgroundColor: colors.primary.light + '12',
-      borderColor: colors.primary.main + '60',
-      borderWidth: 1.5,
+      backgroundColor: colors.chat.surfaceMuted,
     },
     avatarContainer: {
       position: 'relative',
     },
     systemAvatar: {
-      width: 50,
-      height: 50,
-      borderRadius: borderRadius.md,
+      width: 56,
+      height: 56,
+      borderRadius: borderRadius.full,
       alignItems: 'center',
       justifyContent: 'center',
       backgroundColor: colors.primary.main,
     },
     conversationContent: {
       flex: 1,
-      marginLeft: spacing.md,
+      marginLeft: spacing.lg,
     },
     conversationHeader: {
       flexDirection: 'row',
@@ -197,49 +192,49 @@ function createConversationRowStyles(colors: AppColors) {
     officialBadge: {
       backgroundColor: colors.primary.main,
       borderRadius: borderRadius.sm,
-      paddingHorizontal: 6,
-      paddingVertical: 2,
+      paddingHorizontal: 5,
+      paddingVertical: 1,
       marginRight: spacing.xs,
     },
     officialBadgeText: {
       color: colors.primary.contrast,
-      fontSize: 10,
+      fontSize: 9,
       fontWeight: '800',
     },
     userName: {
-      fontWeight: '700',
+      fontWeight: '600',
       color: colors.text.primary,
       fontSize: 16,
-      letterSpacing: 0.3,
+      letterSpacing: 0.2,
     },
     groupIcon: {
-      marginRight: 4,
+      marginRight: 3,
     },
     memberCount: {
-      fontSize: 12,
+      fontSize: 13,
       color: colors.text.secondary,
       marginLeft: 2,
       fontWeight: '500',
     },
     pinnedIcon: {
-      marginLeft: 6,
+      marginLeft: 5,
     },
     groupAvatar: {
-      width: 50,
-      height: 50,
+      width: 56,
+      height: 56,
     },
     groupAvatarPlaceholder: {
-      width: 50,
-      height: 50,
+      width: 56,
+      height: 56,
       borderRadius: borderRadius.md,
       backgroundColor: colors.primary.main,
       alignItems: 'center',
       justifyContent: 'center',
     },
     timeText: {
-      color: colors.text.secondary,
+      color: colors.text.hint,
       fontSize: 12,
-      fontWeight: '500',
+      fontWeight: '400',
     },
     messageRow: {
       flexDirection: 'row',
@@ -250,25 +245,26 @@ function createConversationRowStyles(colors: AppColors) {
       color: colors.text.secondary,
       fontSize: 14,
       fontWeight: '400',
+      lineHeight: 20,
     },
     unreadMessageText: {
       color: colors.text.primary,
       fontWeight: '600',
     },
     unreadBadge: {
-      minWidth: 22,
-      height: 22,
-      borderRadius: 11,
-      backgroundColor: colors.primary.main,
+      minWidth: 20,
+      height: 20,
+      borderRadius: 10,
+      backgroundColor: colors.error.main,
       alignItems: 'center',
       justifyContent: 'center',
       marginLeft: spacing.sm,
-      paddingHorizontal: 6,
+      paddingHorizontal: 5,
     },
     unreadBadgeText: {
-      color: colors.primary.contrast,
+      color: '#FFFFFF',
       fontSize: 12,
-      fontWeight: '800',
+      fontWeight: '700',
     },
   });
 }
@@ -321,12 +317,12 @@ const ConversationListRowInner: React.FC<ConversationListRowProps> = ({
       <View style={styles.avatarContainer}>
         {isSystemChannel ? (
           <View style={styles.systemAvatar}>
-            <MaterialCommunityIcons name="bell-ring" size={24} color={colors.primary.contrast} />
+            <MaterialCommunityIcons name="bell-ring" size={26} color={colors.primary.contrast} />
           </View>
         ) : isGroupChat ? (
           <View style={styles.groupAvatar}>
             {displayAvatar ? (
-              <Avatar source={displayAvatar} size={50} name={displayName} />
+              <Avatar source={displayAvatar} size={56} name={displayName} />
             ) : (
               <View style={styles.groupAvatarPlaceholder}>
                 <MaterialCommunityIcons name="account-group" size={28} color={colors.primary.contrast} />
@@ -334,7 +330,7 @@ const ConversationListRowInner: React.FC<ConversationListRowProps> = ({
             )}
           </View>
         ) : (
-          <Avatar source={displayAvatar} size={50} name={displayName} />
+          <Avatar source={displayAvatar} size={56} name={displayName} />
         )}
       </View>