docs: add routing page (#9550)

- Add a new homepage to `book` project for the routing page
- Move all main doc pages to be under `/v2/learn` (and added redirects + fixed links across docs)
- Other: add admin components to resources dropdown + fixes to search on mobile.

Closes DX-955

Preview: https://docs-v2-git-docs-router-page-medusajs.vercel.app/v2

www/apps/resources/app/recipes/omnichannel/page.mdx

@@ -52,7 +52,7 @@ Another channel that attracts customer sales is social media. You can create a c
     icon: AcademicCapSolid,
   },
   {
-    href: "!docs!/basics/modules",
+    href: "!docs!/learn/basics/modules",
     title: "Create a Module",
     text: "Learn how to create a module.",
     icon: AcademicCapSolid,
@@ -73,13 +73,13 @@ Medusa’s architecture also makes it easier to integrate any third-party servic
 
 <CardList itemsPerRow={2} items={[
   {
-    href: "!docs!/basics/modules",
+    href: "!docs!/learn/basics/modules",
     title: "Create a Module",
     text: "Learn how to create a module.",
     icon: AcademicCapSolid,
   },
   {
-    href: "!docs!/basics/api-routes",
+    href: "!docs!/learn/basics/api-routes",
     title: "Create an API Route",
     text: "Learn how to create an API route.",
     icon: AcademicCapSolid,