fix: 末行单卡片居中 + 卡片高度不一致

- columnWrapperStyle justifyContent 改为 flex-start，末行单卡片靠左
- title 固定 height: 32px（2行 × lineHeight 16），
  使每张卡片 info 区高度相同，消除高度不一致

app/index.tsx

@@ -161,7 +161,7 @@ const styles = StyleSheet.create({
     backgroundColor: '#00AEEC',
     borderRadius: 1,
   },
-  row: { paddingHorizontal: 8, justifyContent:'center' },
+  row: { paddingHorizontal: 8, justifyContent: 'flex-start' },
   leftCol: { marginLeft: 4, marginRight: 2 },
   rightCol: { marginLeft: 2, marginRight: 4 },
   footer: { height: 48, alignItems: 'center', justifyContent: 'center' },

components/VideoCard.tsx

@@ -45,7 +45,7 @@ const styles = StyleSheet.create({
   durationBadge: { position: 'absolute', bottom: 4, right: 4, backgroundColor: 'rgba(0,0,0,0.6)', borderRadius: 3, paddingHorizontal: 4, paddingVertical: 1 },
   durationText: { color: '#fff', fontSize: 10 },
   info: { padding: 6 },
-  title: { fontSize: 12, color: '#212121', lineHeight: 16, marginBottom: 4 },
+  title: { fontSize: 12, color: '#212121', lineHeight: 16, height: 32, marginBottom: 4 },
   meta: { flexDirection: 'row', alignItems: 'center', gap: 2 },
   metaText: { fontSize: 11, color: '#999' },
   owner: { fontSize: 11, color: '#999', marginTop: 2 },