BuildContext used across async gaps in multiple screens

[CrowdTypical]

Description

Several screens and dialogs capture context before an await and use it afterwards. While mounted checks are present in most cases, there are inconsistencies where some paths miss the check.

Affected Files

• lib/widgets/settle_up_dialog.dart — context used after dialog operations
• lib/screens/group_details_screen.dart — _loadData() sets state without mounted guard
• lib/screens/bill_detail_screen.dart — _loadData() in initState may complete after dispose

Recommended Fix

Always capture ScaffoldMessenger.of(context) and Navigator.of(context) before the await, then use the captured reference after.

// Before (unsafe)
await someAsyncOp();
if (mounted) {
  ScaffoldMessenger.of(context).showSnackBar(...);
}

// After (safe)
final messenger = ScaffoldMessenger.of(context);
await someAsyncOp();
if (mounted) {
  messenger.showSnackBar(...);
}

Priority

High — can cause crashes on slow devices or flaky networks.