feat(onboarding): back-button between steps + language switcher on welcome

Back-Button:
- OnboardingNavContext liefert der Shell einen optionalen goBack-Handler
  (kein prop-drilling durch 8 Slides).
- OnboardingShell: chevron-back links neben der Progress-Bar wenn goBack
  gesetzt ist.
- Controller: goToLinearPrevious() + BACK_ALLOWED-Liste. Back nur auf
  privacy/nickname/diga_choice/plan/payment — NICHT welcome (erste),
  done (final), diga_code (eigener onBack), protection (Backend-Step +
  Permission-Flow).

Language-Switcher:
- WelcomeSlide: 4 Sprach-Pills (DE/EN/FR/AR) oben rechts. User kommt
  während Onboarding nicht zu Settings — sonst kein Weg die Sprache
  zu wechseln. setLanguage persistiert + flippt RTL für AR.

apps/rebreak-native/app/onboarding/index.tsx

@@ -11,6 +11,7 @@ import { PlanSlide } from '../../components/onboarding/slides/PlanSlide';
 import { PaymentSlide } from '../../components/onboarding/slides/PaymentSlide';
 import { ProtectionSlide } from '../../components/onboarding/slides/ProtectionSlide';
 import { DoneSlide } from '../../components/onboarding/slides/DoneSlide';
+import { OnboardingNavProvider } from '../../components/onboarding/OnboardingNavContext';
 
 /**
  * Duo-Style Onboarding — single route, state-machine intern.
@@ -97,6 +98,18 @@ export default function OnboardingScreen() {
     setSlide(LINEAR_ORDER[idx + 1]);
   }
 
+  function goToLinearPrevious() {
+    const idx = LINEAR_ORDER.indexOf(slide);
+    if (idx <= 0) return;
+    setSlide(LINEAR_ORDER[idx - 1]);
+  }
+
+  // Back erlaubt nur auf reinen Info-/Auswahl-Slides. NICHT auf:
+  //   welcome (erste), done (final), diga_code (hat eigenen onBack),
+  //   protection (interne Phasen + persistierter Backend-Step + Permission-Flow).
+  const BACK_ALLOWED: Slide[] = ['privacy', 'nickname', 'diga_choice', 'plan', 'payment'];
+  const canGoBack = BACK_ALLOWED.includes(slide);
+
   function exitToApp() {
     router.replace('/(app)');
   }
@@ -135,42 +148,50 @@ export default function OnboardingScreen() {
 
   // Slide-Dispatch ────────────────────────────────────────────────────────────
 
-  switch (slide) {
+  function renderSlide() {
-    case 'welcome':
+    switch (slide) {
-      return <WelcomeSlide onNext={goToLinearNext} current={current} total={total} />;
+      case 'welcome':
-    case 'privacy':
+        return <WelcomeSlide onNext={goToLinearNext} current={current} total={total} />;
-      return <PrivacySlide onNext={goToLinearNext} current={current} total={total} />;
+      case 'privacy':
-    case 'nickname':
+        return <PrivacySlide onNext={goToLinearNext} current={current} total={total} />;
-      return <NicknameSlide onNext={goToLinearNext} current={current} total={total} />;
+      case 'nickname':
-    case 'diga_choice':
+        return <NicknameSlide onNext={goToLinearNext} current={current} total={total} />;
-      return (
+      case 'diga_choice':
-        <DigaChoiceSlide
+        return (
-          onYes={onDigaYes}
+          <DigaChoiceSlide
-          onNo={onDigaNo}
+            onYes={onDigaYes}
-          current={current}
+            onNo={onDigaNo}
-          total={total}
+            current={current}
-        />
+            total={total}
-      );
+          />
-    case 'diga_code':
+        );
-      return (
+      case 'diga_code':
-        <DigaCodeSlide
+        return (
-          onSuccess={onDigaCodeSuccess}
+          <DigaCodeSlide
-          onBack={() => setSlide('diga_choice')}
+            onSuccess={onDigaCodeSuccess}
-          current={current}
+            onBack={() => setSlide('diga_choice')}
-          total={total}
+            current={current}
-        />
+            total={total}
-      );
+          />
-    case 'plan':
+        );
-      return <PlanSlide onChosen={onPlanChosen} current={current} total={total} />;
+      case 'plan':
-    case 'payment':
+        return <PlanSlide onChosen={onPlanChosen} current={current} total={total} />;
-      return (
+      case 'payment':
-        <PaymentSlide onCompleted={goToLinearNext} current={current} total={total} />
+        return (
-      );
+          <PaymentSlide onCompleted={goToLinearNext} current={current} total={total} />
-    case 'protection':
+        );
-      return (
+      case 'protection':
-        <ProtectionSlide onDone={goToLinearNext} current={current} total={total} />
+        return (
-      );
+          <ProtectionSlide onDone={goToLinearNext} current={current} total={total} />
-    case 'done':
+        );
-      return <DoneSlide onEnter={exitToApp} current={current} total={total} />;
+      case 'done':
+        return <DoneSlide onEnter={exitToApp} current={current} total={total} />;
+    }
   }
+
+  return (
+    <OnboardingNavProvider goBack={canGoBack ? goToLinearPrevious : null}>
+      {renderSlide()}
+    </OnboardingNavProvider>
+  );
 }

apps/rebreak-native/components/onboarding/OnboardingNavContext.tsx

@@ -0,0 +1,30 @@
+import { createContext, useContext, type ReactNode } from 'react';
+
+/**
+ * Stellt der OnboardingShell einen optionalen Back-Handler bereit, ohne
+ * `onBack` durch alle 8 Slide-Komponenten prop-drillen zu müssen.
+ *
+ * Controller (app/onboarding/index.tsx) entscheidet pro Slide ob ein Back
+ * möglich ist (welcome = erste Slide, done = final → kein Back) und liefert
+ * entsprechend `goBack` oder `null`.
+ */
+const OnboardingBackContext = createContext<(() => void) | null>(null);
+
+export function OnboardingNavProvider({
+  goBack,
+  children,
+}: {
+  goBack: (() => void) | null;
+  children: ReactNode;
+}) {
+  return (
+    <OnboardingBackContext.Provider value={goBack}>
+      {children}
+    </OnboardingBackContext.Provider>
+  );
+}
+
+/** Gibt den Back-Handler zurück, oder null wenn die aktuelle Slide kein Back erlaubt. */
+export function useOnboardingBack(): (() => void) | null {
+  return useContext(OnboardingBackContext);
+}

apps/rebreak-native/components/onboarding/OnboardingShell.tsx

@@ -1,8 +1,10 @@
 import { ReactNode } from 'react';
-import { ScrollView, View } from 'react-native';
+import { ScrollView, TouchableOpacity, View } from 'react-native';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
+import { Ionicons } from '@expo/vector-icons';
 import { useColors } from '../../lib/theme';
 import { SlideProgress } from './SlideProgress';
+import { useOnboardingBack } from './OnboardingNavContext';
 
 /**
  * Layout-Wrapper für alle Onboarding-Slides.
@@ -32,6 +34,7 @@ export function OnboardingShell({
 }) {
   const colors = useColors();
   const insets = useSafeAreaInsets();
+  const goBack = useOnboardingBack();
 
   return (
     <View style={{ flex: 1, backgroundColor: colors.bg }}>
@@ -40,9 +43,31 @@ export function OnboardingShell({
           paddingTop: insets.top + 12,
           paddingHorizontal: 20,
           paddingBottom: 8,
+          flexDirection: 'row',
+          alignItems: 'center',
+          gap: 12,
         }}
       >
-        <SlideProgress current={current} total={total} />
+        {goBack ? (
+          <TouchableOpacity
+            onPress={goBack}
+            activeOpacity={0.6}
+            hitSlop={{ top: 12, bottom: 12, left: 12, right: 12 }}
+            style={{
+              width: 32,
+              height: 32,
+              borderRadius: 10,
+              backgroundColor: colors.surfaceElevated,
+              alignItems: 'center',
+              justifyContent: 'center',
+            }}
+          >
+            <Ionicons name="chevron-back" size={20} color={colors.text} />
+          </TouchableOpacity>
+        ) : null}
+        <View style={{ flex: 1 }}>
+          <SlideProgress current={current} total={total} />
+        </View>
       </View>
 
       <ScrollView

apps/rebreak-native/components/onboarding/slides/WelcomeSlide.tsx

@@ -1,11 +1,59 @@
-import { Text, View } from 'react-native';
+import { Text, TouchableOpacity, View } from 'react-native';
 import { useTranslation } from 'react-i18next';
 import { Ionicons } from '@expo/vector-icons';
 import { useColors } from '../../../lib/theme';
+import { useLanguageStore, type AppLanguage } from '../../../stores/language';
 import { OnboardingShell } from '../OnboardingShell';
 import { LyraBubble } from '../LyraBubble';
 import { CTABar } from '../CTABar';
 
+const LANGS: { code: AppLanguage; label: string }[] = [
+  { code: 'de', label: 'DE' },
+  { code: 'en', label: 'EN' },
+  { code: 'fr', label: 'FR' },
+  { code: 'ar', label: 'AR' },
+];
+
+/**
+ * Kompakter Sprach-Umschalter — nur auf der Welcome-Slide. Während des
+ * Onboardings kommt der User nicht zu Settings, kann die Sprache also sonst
+ * nirgends ändern. setLanguage persistiert in AsyncStorage + flippt RTL für AR.
+ */
+function LanguagePills({ colors }: { colors: import('../../../lib/theme').ColorScheme }) {
+  const language = useLanguageStore((s) => s.language);
+  const setLanguage = useLanguageStore((s) => s.setLanguage);
+  return (
+    <View style={{ flexDirection: 'row', gap: 8, justifyContent: 'flex-end' }}>
+      {LANGS.map((l) => {
+        const active = language === l.code;
+        return (
+          <TouchableOpacity
+            key={l.code}
+            onPress={() => setLanguage(l.code)}
+            activeOpacity={0.7}
+            style={{
+              paddingHorizontal: 12,
+              paddingVertical: 6,
+              borderRadius: 8,
+              backgroundColor: active ? colors.brandOrange : colors.surfaceElevated,
+            }}
+          >
+            <Text
+              style={{
+                fontFamily: 'Nunito_700Bold',
+                fontSize: 13,
+                color: active ? '#ffffff' : colors.textMuted,
+              }}
+            >
+              {l.label}
+            </Text>
+          </TouchableOpacity>
+        );
+      })}
+    </View>
+  );
+}
+
 /**
  * Slide 1: Lyra stellt sich vor + erklärt die Mission in einem Satz.
  * Hat den langen Empathie-Touch, weil's der erste Eindruck nach Signup ist.
@@ -28,6 +76,10 @@ export function WelcomeSlide({
       total={total}
       cta={<CTABar primaryLabel={t('onboarding.welcome.cta_primary')} onPrimary={onNext} />}
     >
+      <View style={{ marginBottom: 16 }}>
+        <LanguagePills colors={colors} />
+      </View>
+
       <LyraBubble text={t('onboarding.lyra.welcome.body')} emotion="happy" />
 
       <View style={{ marginTop: 28, gap: 12 }}>