fix: centralize public hostname into single PUBLIC_HOST env var

All public-facing URLs (Logto OIDC, redirect URIs, dashboard links) now
derive from PUBLIC_HOST in .env instead of scattered localhost references.
Resolves Docker networking ambiguity where localhost inside containers
doesn't reach the host machine.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/Layout.tsx

@@ -162,7 +162,7 @@ export function Layout() {
         <Sidebar.FooterLink
           icon={<ObsIcon />}
           label="View Dashboard"
-          onClick={() => window.open('http://localhost:8082', '_blank', 'noopener')}
+          onClick={() => window.open(`http://${window.location.hostname}:8082`, '_blank', 'noopener')}
         />
 
         {/* User info + logout */}