docs: add "Overlapping IPs for Resources" use case (#828)

Adds the how-to under the reorganized /use-cases/remote-access group
(stacked on the Use Cases reorg). Walks through the decision ladder for
two sites sharing one internal IP, ending with the per-site TCP proxy
pattern on each routing peer.

src/components/NavigationDocs.jsx

@@ -847,6 +847,10 @@ export const docsNavigation = [
             title: 'Exit Nodes',
             href: '/use-cases/remote-access/exit-nodes',
           },
+          {
+            title: 'Overlapping IPs for Resources',
+            href: '/use-cases/remote-access/overlapping-ips-for-resources',
+          },
           {
             title: 'Reach Services on the Routing Peer',
             href: '/use-cases/remote-access/reach-services-on-the-routing-peer',