Hide spending by category when only one category exists

Both the doughnut chart and top categories table are now hidden
when there's only a single category, as they provide no useful
breakdown in that case. The net cash flow chart expands to full
width when the category chart is hidden.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

MoneyMap/Pages/Index.cshtml

@@ -117,6 +117,8 @@
     </div>
 </div>
 <div class="row g-3 my-2">
+    @if (Model.TopCategories.Count > 1)
+    {
     <div class="col-lg-6">
         <div class="card shadow-sm h-100">
             <div class="card-header">Spending by category (last 90 days)</div>
@@ -125,7 +127,8 @@
             </div>
         </div>
     </div>
-    <div class="col-lg-6">
+    }
+    <div class="@(Model.TopCategories.Count > 1 ? "col-lg-6" : "col-lg-12")">
         <div class="card shadow-sm h-100">
             <div class="card-header">Net cash flow (last 30 days)</div>
             <div class="card-body">
@@ -206,7 +209,7 @@
     </div>
 }
 
-@if (Model.TopCategories.Any())
+@if (Model.TopCategories.Count > 1)
 {
     <div class="card shadow-sm mb-3">
         <div class="card-header">