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/pos/page.mdx

@@ -60,7 +60,7 @@ To search through product variants by their barcode, create a custom API Route a
       icon: AcademicCapSolid,
     },
     {
-      href: "!docs!/basics/api-routes",
+      href: "!docs!/learn/basics/api-routes",
       title: "Create API Route",
       text: "Learn how to create an API Route.",
       icon: AcademicCapSolid,
@@ -167,7 +167,7 @@ You can also create custom modules to provide features for a better customer exp
       icon: AcademicCapSolid,
     },
     {
-      href: "!docs!/basics/modules",
+      href: "!docs!/learn/basics/modules",
       title: "Create a Module",
       text: "Learn how to create a module.",
       icon: AcademicCapSolid,