feat(frontend): show active app domain with click-to-copy

Surface the domain the app is actually reachable on right now (verified
custom domain, else the platform subdomain) as a single "Application
Domain" field. Clicking it copies the address to the clipboard and shows
a "Copied" toast. Centralizes the active-domain logic so the page header
and the verified-custom-domain block stay in sync, and always loads
domain-info so the platform host is correct even without a custom domain.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/i18n/dictionaries/en.ts

@@ -1286,6 +1286,7 @@ const en: Dictionary = {
       uploadToStart: 'Upload source code and click Deploy to get started',
       sourceCode: 'Source Code', replace: 'Replace', uploadSourceClick: 'Upload source code and click Deploy to get started',
       customDomain: 'Custom Domain', addCustomDomain: 'Add Custom Domain', setUpCustomDomain: 'Set Up Custom Domain',
+      appDomain: 'Application Domain', copyDomainHint: 'Click to copy',
       platformDomain: 'Platform Domain', domainPlaceholder: 'example.com or www.example.com', dnsSetupGuide: 'DNS Setup Guide',
       removeCustomDomain: 'Remove Custom Domain',
       resourcesScaling: 'Resources & Scaling', monitor: 'Monitor', hide: 'Hide', show: 'Show',