Hide customer action buttons (Submit/Add to bag) when in admin editing mode

Added isAdminEditing prop to DesignCanvas component. When true, hides the
"Submit for Approval" and "Add to bag" buttons since these are customer-facing
actions. The admin edit page now only shows the design canvas and the
"Send to Customer for Review" button.

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

src/app/admin/designs/[id]/edit/page.tsx

@@ -109,7 +109,7 @@ export default function EditDesignPage({ params }: { params: { id: string } }) {
         </div>
 
         {/* Full Design Canvas */}
-        <DesignCanvas product={design.product} />
+        <DesignCanvas product={design.product} isAdminEditing={true} />
       </div>
     </div>
   );