fix(i18n): add common.close to en + de locales

The device-sync migration modal uses t('common.close') for its dismiss
button, but the key lived only inside scoped namespaces (where it had
different translations like "Verstanden" / "Got it"). Add the
straightforward "Schließen" / "Close" under common so the migration
modal shows the right label.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/en.ts

@@ -376,6 +376,7 @@ export const enTranslation = {
     downloadZip: 'Download (ZIP)',
     back: 'Back',
     cancel: 'Cancel',
+    close: 'Close',
     save: 'Save',
     delete: 'Delete',
     use: 'Use',