feat(performance): migrate FlatList to FlashList and add animations

Replace FlatList with FlashList across all message screens (ChatScreen, MessageListScreen, NotificationsScreen, HomeScreen) for improved list virtualization performance. Use `drawDistance={250}` instead of manual pagination. Simplify React.memo comparisons in MessageBubble and SegmentRenderer by removing function prop checks to prevent unnecessary re-renders.

Add AsyncStorage persistence for lastSystemMessageAt to avoid showing current time on first render. Include enter animations (fade and slide) for CreateGroupScreen and modernize UI styling to flat design.

BREAKING CHANGE: Upgrade @shopify/flash-list from 2.0.2 to ^2.3.1

src/components/business/PostCard/PostCard.tsx

@@ -600,8 +600,14 @@ const PostCardInner: React.FC<PostCardProps> = (normalizedProps) => {
             <Text style={styles.gridUsername} numberOfLines={1}>{author?.nickname || '匿名用户'}</Text>
           </TouchableOpacity>
           <View style={styles.gridLikeArea}>
-            <MaterialCommunityIcons name="thumb-up-outline" size={14} color={colors.text.secondary} />
-            <Text style={styles.gridLikeCount}>{formatNumber(post.likes_count || 0)}</Text>
+            <MaterialCommunityIcons
+              name={post.is_liked ? 'thumb-up' : 'thumb-up-outline'}
+              size={14}
+              color={post.is_liked ? colors.primary.main : colors.text.secondary}
+            />
+            <Text style={[styles.gridLikeCount, post.is_liked && { color: colors.primary.main }]}>
+              {formatNumber(post.likes_count || 0)}
+            </Text>
           </View>
         </View>
       </TouchableOpacity>