fix: improve mobile responsiveness of cospend page

Reduced padding on mobile screens (max-width: 600px) to prevent horizontal overflow and ensure header spans full width. Updated BarChart, DebtBreakdown, EnhancedBalance components and recent activity section.

src/lib/components/BarChart.svelte

@@ -323,6 +323,12 @@
     }
   }
 
+  @media (max-width: 600px) {
+    .chart-container {
+      padding: 0.75rem;
+    }
+  }
+
   canvas {
     max-width: 100%;
     height: 100% !important;