feat: check for existing orders before user deletion and offer to lock instead

shop/lib/actions/users.ts

@@ -92,6 +92,21 @@ export async function createUser(data: { email: string; role?: 'admin' | 'partne
 export async function deleteUser(id: string) {
   try {
     const admin = createAdminClient();
+    
+    // Check if user has orders (documents/belege)
+    const { count, error: countError } = await admin
+      .from('orders')
+      .select('*', { count: 'exact', head: true })
+      .eq('user_id', id);
+      
+    if (countError) {
+      console.error('Failed to count user orders:', countError);
+    }
+    
+    if (count && count > 0) {
+      throw new Error('Auf diesen User gibt es bereits Belege. Sperren möglich.');
+    }
+    
     // Delete from public.users first to satisfy foreign key constraints
     const { error: dbError } = await admin.from('users').delete().eq('id', id);
     if (dbError) {