Add percentage of total to top expense categories on dashboard

Show what percentage of total expenses each category represents in the top categories table. This helps quickly identify which categories consume the largest portion of spending.

Changes:
- Add PercentageOfTotal property to TopCategoryRow
- Calculate percentage based on total expenses in the period
- Display percentage as a badge in the table (e.g., "23.5%")
- Add new "% of Total" column header
- Format to 1 decimal place for clarity

Example: If "Groceries" is $500 and total expenses are $2000, it shows 25.0%

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

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

MoneyMap/Pages/Index.cshtml

@@ -71,6 +71,7 @@
                     <tr>
                         <th>Category</th>
                         <th class="text-end">Total Spend</th>
+                        <th class="text-end">% of Total</th>
                         <th class="text-end">Txns</th>
                     </tr>
                 </thead>
@@ -84,6 +85,9 @@
                                 </a>
                             </td>
                             <td class="text-end">@c.TotalSpend.ToString("C")</td>
+                            <td class="text-end">
+                                <span class="badge bg-secondary">@c.PercentageOfTotal.ToString("F1")%</span>
+                            </td>
                             <td class="text-end">@c.Count</td>
                         </tr>
                     }

MoneyMap/Pages/Index.cshtml.cs

@@ -44,6 +44,7 @@ namespace MoneyMap.Pages
             public string Category { get; set; } = "";
             public decimal TotalSpend { get; set; }
             public int Count { get; set; }
+            public decimal PercentageOfTotal { get; set; }
         }
 
         public class RecentTxnRow
@@ -176,20 +177,30 @@ namespace MoneyMap.Pages
         {
             var since = DateTime.UtcNow.Date.AddDays(-lastDays);
 
-            return await _db.Transactions
+            // Get all expense transactions for the period
+            var expenseTransactions = await _db.Transactions
                 .Where(t => t.Date >= since && t.Amount < 0)
                 .ExcludeTransfers() // Exclude credit card payments and transfers
+                .ToListAsync();
+
+            // Calculate total spend
+            var totalSpend = expenseTransactions.Sum(t => -t.Amount);
+
+            // Group by category and calculate percentages
+            var topCategories = expenseTransactions
                 .GroupBy(t => t.Category ?? "")
                 .Select(g => new IndexModel.TopCategoryRow
                 {
                     Category = g.Key,
                     TotalSpend = g.Sum(x => -x.Amount),
-                    Count = g.Count()
+                    Count = g.Count(),
+                    PercentageOfTotal = totalSpend > 0 ? (g.Sum(x => -x.Amount) / totalSpend) * 100 : 0
                 })
                 .OrderByDescending(x => x.TotalSpend)
                 .Take(count)
-                .AsNoTracking()
-                .ToListAsync();
+                .ToList();
+
+            return topCategories;
         }
     }