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/config.ts

@@ -22,7 +22,7 @@ export async function fetchConfig(): Promise<AppConfig> {
 
   // Fallback to env vars (Vite dev mode)
   cached = {
-    logtoEndpoint: import.meta.env.VITE_LOGTO_ENDPOINT || 'http://localhost:3001',
+    logtoEndpoint: import.meta.env.VITE_LOGTO_ENDPOINT || `http://${window.location.hostname}:3001`,
     logtoClientId: import.meta.env.VITE_LOGTO_CLIENT_ID || '',
     logtoResource: import.meta.env.VITE_LOGTO_RESOURCE || '',
     scopes: [