Make responsive tab bar position the default

- Reorder options: responsive first, then top, then bottom
- Change default tabBarPosition from 'top' to 'responsive'

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/admin/ThemeSettings.tsx

@@ -186,9 +186,9 @@ export default function ThemeSettings() {
     ];
 
     const tabBarPositions: { id: TabBarPosition; label: string; description: string }[] = [
+        { id: 'responsive', label: t.theme.tabBarPositions?.responsive || 'Responsivo', description: t.theme.tabBarPositions?.responsiveDesc || 'In alto su desktop, in basso su mobile' },
         { id: 'top', label: t.theme.tabBarPositions?.top || 'Sopra', description: t.theme.tabBarPositions?.topDesc || 'Barra dei tab sempre in alto' },
         { id: 'bottom', label: t.theme.tabBarPositions?.bottom || 'Sotto', description: t.theme.tabBarPositions?.bottomDesc || 'Barra dei tab sempre in basso' },
-        { id: 'responsive', label: t.theme.tabBarPositions?.responsive || 'Responsivo', description: t.theme.tabBarPositions?.responsiveDesc || 'In alto su desktop, in basso su mobile' },
     ];
 
     const palettes: { id: ColorPalette; label: string; description: string }[] = [