Add persistent language switcher across all learn/parent pages

useNativeLanguage: Now has setNativeLang() that persists to localStorage.
Language selection carries across all pages automatically.

LanguageSwitcher: Compact dropdown component added to learn/layout.tsx
and parent/layout.tsx — visible on every sub-page (top-right).

Parent portal: Language dropdown syncs both UI language and native
language. Parents can switch language mid-session (e.g. when both
parents speak different languages).

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

studio-v2/components/learn/LanguageSwitcher.tsx

@@ -0,0 +1,58 @@
+'use client'
+
+import React from 'react'
+
+interface LanguageSwitcherProps {
+  currentLang: string
+  onLangChange: (lang: string) => void
+  isDark: boolean
+  compact?: boolean
+}
+
+const LANGS = [
+  { code: 'de', label: 'DE' },
+  { code: 'en', label: 'EN' },
+  { code: 'tr', label: 'TR' },
+  { code: 'ar', label: 'AR' },
+  { code: 'uk', label: 'UK' },
+  { code: 'ru', label: 'RU' },
+  { code: 'pl', label: 'PL' },
+]
+
+/**
+ * Compact language switcher for exercise pages.
+ * Shows as dropdown or pill buttons depending on compact prop.
+ */
+export function LanguageSwitcher({ currentLang, onLangChange, isDark, compact = true }: LanguageSwitcherProps) {
+  if (compact) {
+    return (
+      <select
+        value={currentLang}
+        onChange={e => onLangChange(e.target.value)}
+        className={`text-xs px-2 py-1 rounded-lg border-0 cursor-pointer ${
+          isDark ? 'bg-white/10 text-white/70' : 'bg-slate-100 text-slate-600'
+        }`}
+      >
+        {LANGS.map(l => <option key={l.code} value={l.code}>{l.label}</option>)}
+      </select>
+    )
+  }
+
+  return (
+    <div className="flex gap-1">
+      {LANGS.map(l => (
+        <button
+          key={l.code}
+          onClick={() => onLangChange(l.code)}
+          className={`px-2 py-1 rounded-lg text-xs font-medium transition-all ${
+            currentLang === l.code
+              ? 'bg-blue-500 text-white'
+              : isDark ? 'bg-white/5 text-white/40 hover:bg-white/10' : 'bg-slate-100 text-slate-400 hover:bg-slate-200'
+          }`}
+        >
+          {l.label}
+        </button>
+      ))}
+    </div>
+  )
+}