docs: add self-hosted Environment Variables page to sidebar nav (#799)

The /selfhosted/environment-variables reference page had no inbound
links and was only reachable by direct URL or search. Add it under
Maintenance, after Configuration Files.

src/components/NavigationDocs.jsx

@@ -549,6 +549,10 @@ export const docsNavigation = [
             title: 'Configuration Files',
             href: '/selfhosted/maintenance/configuration-files',
           },
+          {
+            title: 'Environment Variables',
+            href: '/selfhosted/environment-variables',
+          },
           {
             title: 'Scaling Your Deployment',
             href: '/selfhosted/maintenance/scaling/scaling-your-self-hosted-deployment',
@@ -1002,7 +1006,11 @@ function NavigationGroup({ group, className, hasChildren }) {
           }
           setIsOpen(!isOpen)
           if (!isOpen) {
-            if (!isActiveGroup && !isInsideMobileNavigation && group.links[0]?.href)
+            if (
+              !isActiveGroup &&
+              !isInsideMobileNavigation &&
+              group.links[0]?.href
+            )
               router.push(group.links[0].href)
             setActiveHighlight()
           } else {