Add "reste à dépenser" tile to the dashboard

Shows the total remaining depense budget for the selected period,
above the breakdown table — reuses the totals.reste figure already
computed per section, no new query.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

resources/views/livewire/dashboard/index.blade.php

@@ -22,6 +22,11 @@
         </div>
     </div>
 
+    <div class="bg-surface shadow rounded-lg p-4 max-w-xs">
+        <p class="text-xs text-text-muted">Reste à dépenser</p>
+        <p class="mt-1 text-lg font-semibold text-negative">{{ number_format($sections['depense']['totals']['reste'], 2, ',', ' ') }} €</p>
+    </div>
+
     @php
         $colors = [
             'revenu' => ['bg' => 'bg-positive-fill', 'row' => 'bg-positive-surface/40'],