Fix ToHashSet() compatibility issue in Receipts page

Changed from using .ToHashSet() extension method (which may not be
available in some EF Core versions) to .ToListAsync() followed by
creating a HashSet from the list.

This ensures compatibility across different EF Core versions while
maintaining the same performance characteristics.

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

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

MoneyMap/Pages/Receipts.cshtml.cs

@@ -171,10 +171,12 @@ namespace MoneyMap.Pages
             }).ToList();
 
             // Load matching transactions for each unmapped receipt
-            var transactionsWithReceipts = await _db.Receipts
+            var transactionsWithReceiptsList = await _db.Receipts
                 .Where(r => r.TransactionId != null)
                 .Select(r => r.TransactionId!.Value)
-                .ToHashSet();
+                .ToListAsync();
+
+            var transactionsWithReceipts = new HashSet<long>(transactionsWithReceiptsList);
 
             var unmappedReceipts = Receipts.Where(r => !r.TransactionId.HasValue).ToList();