Add Scandinavian i18n (da/sv/nb) via DeepL pipeline.

Integrate new locale bundles, language cycling in the UI, SEO hreflang tags, and localized beta flyer HTML variants with scripts for batch translation and key validation.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/components/LogbookDashboard.tsx

@@ -1,5 +1,6 @@
 import React, { useState, useEffect, useRef, useMemo } from 'react'
 import { useTranslation } from 'react-i18next'
+import { getNextLanguage } from '../utils/i18nLanguages.js'
 import { useSyncIndicator } from '../hooks/useSyncIndicator.js'
 import { fetchLogbooks, createLogbook, deleteLogbook, updateLogbookTitle, type DecryptedLogbook } from '../services/logbook.js'
 import LogbookRoleBadge from './LogbookRoleBadge.tsx'
@@ -193,8 +194,7 @@ export default function LogbookDashboard({ onSelectLogbook, onLogout, onOpenProf
   }
 
   const toggleLanguage = () => {
-    const nextLang = i18n.language.startsWith('de') ? 'en' : 'de'
-    i18n.changeLanguage(nextLang)
+    i18n.changeLanguage(getNextLanguage(i18n.language))
   }
 
   const ownedLogbooks = logbooks.filter((lb) => !lb.isShared)