Fix Supabase client proxy

src/hooks/useUnitPreferences.ts

@@ -101,6 +101,8 @@ export function useUnitPreferences() {
               user_id: user.id,
               unit_preferences: newPreferences as unknown as Json,
               updated_at: new Date().toISOString()
+            }, {
+              onConflict: 'user_id'
             });
           
           if (error) {