Filter transactions by ±10% amount tolerance for receipt mapping

Changed amount matching from a fixed ±$0.10 tolerance to a percentage-based ±10% tolerance. This dramatically narrows down the transaction list for manual mapping, often to just 1-2 transactions.

Changes:
- Manual mapping: Filters candidates to ±10% of receipt total
- Manual mapping: Green highlighting for very close matches (±2%)
- Auto-mapping: Uses same ±10% tolerance for filtering
- UI: Updated help text to explain the filtering

Example: A $100 receipt will only show transactions between $90-$110, making it much easier to find the correct match.

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

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

MoneyMap/Pages/Receipts.cshtml

@@ -314,7 +314,7 @@
                                     {
                                         <span>Showing recent transactions without receipts.</span>
                                     }
-                                    Rows highlighted in <span class="badge bg-success">green</span> have matching amounts.
+                                    Rows highlighted in <span class="badge bg-success">green</span> have matching amounts (within ±2%). Only showing transactions within ±10% of receipt total.
                                 </div>
                                 <input type="hidden" id="transactionId@(r.Id)" name="transactionId" required />
                                 <div id="transactionListContainer@(r.Id)" style="max-height: 400px; overflow-y: auto; border: 1px solid #dee2e6; border-radius: 0.25rem;">

MoneyMap/Pages/Receipts.cshtml.cs

@@ -294,6 +294,23 @@ namespace MoneyMap.Pages
                     .ToList();
             }
 
+            // Filter by amount (±10% tolerance) if receipt has a total
+            if (receipt.Total.HasValue)
+            {
+                var receiptTotal = Math.Abs(receipt.Total.Value);
+                var tolerance = receiptTotal * 0.10m; // 10% tolerance
+                var minAmount = receiptTotal - tolerance;
+                var maxAmount = receiptTotal + tolerance;
+
+                candidates = candidates
+                    .Where(t =>
+                    {
+                        var transactionAmount = Math.Abs(t.Amount);
+                        return transactionAmount >= minAmount && transactionAmount <= maxAmount;
+                    })
+                    .ToList();
+            }
+
             // Calculate match scores and mark close amount matches
             var options = candidates.Select(t =>
             {
@@ -308,12 +325,13 @@ namespace MoneyMap.Pages
                     IsAmountMatch = false
                 };
 
-                // Check if amount matches within tolerance
+                // Check if amount matches within tighter tolerance for highlighting (±2%)
                 if (receipt.Total.HasValue)
                 {
                     var receiptTotal = Math.Abs(receipt.Total.Value);
                     var transactionAmount = Math.Abs(t.Amount);
-                    option.IsAmountMatch = Math.Abs(transactionAmount - receiptTotal) <= 0.10m;
+                    var tightTolerance = receiptTotal * 0.02m; // 2% for green highlighting
+                    option.IsAmountMatch = Math.Abs(transactionAmount - receiptTotal) <= tightTolerance;
                 }
 
                 return option;

MoneyMap/Services/ReceiptAutoMapper.cs

@@ -130,14 +130,20 @@ namespace MoneyMap.Services
             // Get candidates
             var candidates = await query.ToListAsync();
 
-            // If we have a total amount, filter by amount match
+            // If we have a total amount, filter by amount match (±10% tolerance)
             if (receipt.Total.HasValue)
             {
-                // Allow for slight variations in amount (e.g., due to rounding)
-                // Match if transaction amount is within $0.10 of receipt total
                 var receiptTotal = Math.Abs(receipt.Total.Value);
+                var tolerance = receiptTotal * 0.10m; // 10% tolerance
+                var minAmount = receiptTotal - tolerance;
+                var maxAmount = receiptTotal + tolerance;
+
                 candidates = candidates
-                    .Where(t => Math.Abs(Math.Abs(t.Amount) - receiptTotal) <= 0.10m)
+                    .Where(t =>
+                    {
+                        var transactionAmount = Math.Abs(t.Amount);
+                        return transactionAmount >= minAmount && transactionAmount <= maxAmount;
+                    })
                     .ToList();
             }