Fix 5 broken internal links across docs (#596)

- Fix case mismatch: /get-started/install/iOS → /ios (would 404 on Linux)
- Remove literal /index from /manage/dns/index → /manage/dns
- Add missing /by-scenario/ segment to 3 network-routes links

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/pages/use-cases/homelab/index.mdx

@@ -30,7 +30,7 @@ For connecting entire home networks (accessing devices that don't have NetBird i
             description: 'Set up VPN-to-Site access to reach home network devices from anywhere',
         },
         {
-            href: '/manage/network-routes/use-cases/site-to-site-home',
+            href: '/manage/network-routes/use-cases/by-scenario/site-to-site-home',
             name: 'Connect Home Networks',
             description: 'Link multiple home networks together using Site-to-Site routing',
         },

src/pages/use-cases/site-to-site/index.mdx

@@ -118,12 +118,12 @@ All scenarios use a routing peer—a device running NetBird that forwards traffi
     title="Site-to-Site Guides (Network Routes)"
     items={[
         {
-            href: '/manage/network-routes/use-cases/site-to-site-home',
+            href: '/manage/network-routes/use-cases/by-scenario/site-to-site-home',
             name: 'Connect Home Networks',
             description: 'Link multiple home networks so devices can communicate across locations',
         },
         {
-            href: '/manage/network-routes/use-cases/site-to-site-office',
+            href: '/manage/network-routes/use-cases/by-scenario/site-to-site-office',
             name: 'Connect Office Networks',
             description: 'Connect branch offices to headquarters and enable cross-site communication',
         },