Fix navigation padding to prevent overflow

Add proper right margin to selected navigation items to prevent them from overflowing outside the sidebar boundaries.

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

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

src/components/layout/DashboardLayout.tsx

@@ -112,6 +112,8 @@ const DashboardLayout = ({ children }: DashboardLayoutProps) => {
                 '&.Mui-selected': {
                   backgroundColor: 'primary.main',
                   color: 'primary.contrastText',
+                  ml: 1,
+                  mr: 2,
                   '&:hover': {
                     backgroundColor: 'primary.dark',
                   },