docs: fix outdated links (#10040)

www/apps/book/app/learn/customization/custom-features/api-route/page.mdx

@@ -16,7 +16,7 @@ This chapter covers how to define an API route that creates a brand as the last
   items={[
     {
       text: "createBrandWorkflow",
-      link: "/customization/custom-features/workflow"
+      link: "/learn/customization/custom-features/workflow"
     }
   ]}
 />

www/apps/book/app/learn/customization/custom-features/workflow/page.mdx

@@ -34,7 +34,7 @@ This is even more useful when you create workflows with many steps, or integrate
   items={[
     {
       text: "Brand Module",
-      link: "/customization/custom-features/module"
+      link: "/learn/customization/custom-features/module"
     }
   ]}
 />