docs: Improve drop indicator and touchable example colors (#557)

## Summary

Two small Grid example colour fixes (visible on the docs site):

- **Drop indicator (custom-style example)** —
`--ifm-color-primary-lightest` was too bright in dark mode; now a
transparent fill with a `--ifm-color-primary` border.
- **Touchable** — the delete button blended into the card
(`--ifm-color-primary-light`); now translucent white, with reordering
persisted via `onDragEnd`.

Verified in light and dark mode.

Author: MatiPl01

packages/docs/src/examples/DropIndicatorCustomStyle.tsx

@@ -42,10 +42,11 @@ const styles = StyleSheet.create({
     padding: 10
   },
   dropIndicator: {
-    backgroundColor: 'var(--ifm-color-primary-lightest)',
+    backgroundColor: 'transparent',
     borderColor: 'var(--ifm-color-primary)',
+    borderRadius: 10,
     borderStyle: 'solid',
-    borderWidth: 5
+    borderWidth: 4
   },
   text: {
     color: 'white',

packages/docs/src/examples/Touchable.tsx

@@ -35,6 +35,7 @@ export default function TouchableExample() {
         data={data}
         renderItem={renderItem}
         rowGap={10}
+        onDragEnd={({ data: newData }) => setData(newData)}
       />
       {data.length === 0 && (
         <View style={styles.emptyContainer}>
@@ -59,7 +60,7 @@ const styles = StyleSheet.create({
     padding: 10
   },
   deleteButton: {
-    backgroundColor: 'var(--ifm-color-primary-light)',
+    backgroundColor: 'rgba(255, 255, 255, 0.3)',
     borderRadius: 10,
     padding: 8
   },