Add Schulsprache (school language) as second language setting

- LanguageContext: new schoolLanguage + setSchoolLanguage
- LanguageDropdown: two tabs (Muttersprache / Schulsprache) with flag selection
- UnitBuilder: defaults target language to schoolLanguage
- Stored in bp_school_language localStorage (default: de)
- Shows school flag badge next to main language when different

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

studio-v2/lib/LanguageContext.tsx

@@ -6,6 +6,8 @@ import {
   defaultLanguage,
   getStoredLanguage,
   setStoredLanguage,
+  getStoredSchoolLanguage,
+  setStoredSchoolLanguage,
   translations,
   availableLanguages,
   isRTL,
@@ -14,6 +16,8 @@ import {
 interface LanguageContextType {
   language: Language
   setLanguage: (lang: Language) => void
+  schoolLanguage: Language
+  setSchoolLanguage: (lang: Language) => void
   t: (key: string) => string
   isRTL: boolean
   availableLanguages: typeof availableLanguages
@@ -23,38 +27,42 @@ const LanguageContext = createContext<LanguageContextType | null>(null)
 
 export function LanguageProvider({ children }: { children: ReactNode }) {
   const [language, setLanguageState] = useState<Language>(defaultLanguage)
+  const [schoolLanguage, setSchoolLangState] = useState<Language>(defaultLanguage)
   const [mounted, setMounted] = useState(false)
 
-  // Nach dem ersten Render: Sprache aus localStorage laden
   useEffect(() => {
-    const stored = getStoredLanguage()
-    setLanguageState(stored)
+    setLanguageState(getStoredLanguage())
+    setSchoolLangState(getStoredSchoolLanguage())
     setMounted(true)
   }, [])
 
-  // Sprache setzen und speichern
   const setLanguage = (lang: Language) => {
     setLanguageState(lang)
     setStoredLanguage(lang)
-    // Optional: document.dir fuer RTL setzen
     if (typeof document !== 'undefined') {
       document.documentElement.dir = isRTL(lang) ? 'rtl' : 'ltr'
       document.documentElement.lang = lang
     }
   }
 
+  const setSchoolLanguage = (lang: Language) => {
+    setSchoolLangState(lang)
+    setStoredSchoolLanguage(lang)
+  }
+
   // Uebersetzungsfunktion (Fallback: en → de → key)
   const t = (key: string): string => {
     return translations[language]?.[key] || translations['en']?.[key] || translations['de']?.[key] || key
   }
 
-  // Waehrend SSR: Default anzeigen
   if (!mounted) {
     return (
       <LanguageContext.Provider
         value={{
           language: defaultLanguage,
           setLanguage: () => {},
+          schoolLanguage: defaultLanguage,
+          setSchoolLanguage: () => {},
           t: (key) => translations[defaultLanguage]?.[key] || key,
           isRTL: false,
           availableLanguages,
@@ -70,6 +78,8 @@ export function LanguageProvider({ children }: { children: ReactNode }) {
       value={{
         language,
         setLanguage,
+        schoolLanguage,
+        setSchoolLanguage,
         t,
         isRTL: isRTL(language),
         availableLanguages,