Fix voice picker modal - add minHeight for proper scrolling

- Changed voiceList style from flex: 1 to minHeight: 300
- Added backgroundColor and borderRadius for better visibility
- Now all 35+ voices are visible and scrollable in the DEV modal

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/(tabs)/voice.tsx

@@ -1394,9 +1394,11 @@ const styles = StyleSheet.create({
     fontWeight: '600',
   },
   voiceList: {
-    flex: 1,
-    maxHeight: 400,
+    minHeight: 300,
+    maxHeight: 450,
     padding: Spacing.sm,
+    backgroundColor: AppColors.background,
+    borderRadius: BorderRadius.md,
   },
   voiceSectionTitle: {
     fontSize: FontSizes.sm,