docs: rename Network Routes to Routes, deprecate, and relocate Browser Client Architecture (#792)

* docs: rename Network Routes to Routes, deprecate, and relocate Browser Client Architecture

- Rename the docs sidebar entry "Network Routes" to "Routes" and the page H1
- Add a deprecation note to the Routes page: all use cases except exit nodes
  have moved to Networks; reconcile the body framing accordingly
- Move Browser Client Architecture under Peers > Browser Client
  (/manage/peers/browser-client/architecture), nest the nav, add a redirect,
  and update cross-links
- Shrink the site-to-site Architecture diagram boxes to fit their content

* docs: rename Routes nav 'Concept' link to 'Overview'

src/pages/introduction.mdx

@@ -102,7 +102,7 @@ It literally takes less than 5 minutes to deploy a secure point-to-point VPN wit
         'Compare NetBird Cloud with the self-hosted version and decide which deployment fits your needs.',
     },
     {
-      href: '/about-netbird/browser-client-architecture',
+      href: '/manage/peers/browser-client/architecture',
       name: 'Browser Client Architecture',
       description:
         'Understand how the Browser Client enables secure remote access directly from web browsers using WebAssembly.',