docs: add "Private Proxy Without Public Inbound Ports" use case (#803)

Document running a BYOP proxy in private mode with no public inbound
ports by disabling proxy ACME, issuing the wildcard TLS certificate
externally over DNS-01, and serving it as a static certificate that the
proxy hot-reloads on renewal.

Adds the page under reverse-proxy/use-cases with a new Use Cases nav
group, plus cross-links from the Bring Your Own Proxy page (port-443
prerequisite + TLS table) and the Reverse Proxy overview (static cert
mode).

src/components/NavigationDocs.jsx

@@ -347,6 +347,16 @@ export const docsNavigation = [
             title: 'Troubleshooting',
             href: '/manage/reverse-proxy/troubleshooting',
           },
+          {
+            title: 'Use Cases',
+            isOpen: false,
+            links: [
+              {
+                title: 'No Public Inbound',
+                href: '/manage/reverse-proxy/use-cases/private-no-inbound',
+              },
+            ],
+          },
         ],
       },
       {