implement state management and bottom navigation

.env.example

@@ -0,0 +1 @@
+EXPO_PUBLIC_CLERK_PUBLISHABLE_KEY=YOUR_CLERK_PUBLISHABLE_KEY

app/(tabs)/_layout.tsx

@@ -0,0 +1,36 @@
+import { BottomTabBar } from "@/components/bottom-tab-bar";
+import { useLanguageStore } from "@/store/UseLanguageStore";
+import { useAuth } from "@clerk/expo";
+import { Redirect, Tabs } from "expo-router";
+
+export default function TabsLayout() {
+  const { isLoaded, isSignedIn } = useAuth();
+  const hasHydratedLanguage = useLanguageStore((state) => state.hasHydrated);
+  const selectedLanguageId = useLanguageStore((state) => state.selectedLanguageId);
+
+  if (!isLoaded || !hasHydratedLanguage) {
+    return null;
+  }
+
+  if (!isSignedIn) {
+    return <Redirect href="/onboarding" />;
+  }
+
+  if (!selectedLanguageId) {
+    return <Redirect href="/LanguageSelection" />;
+  }
+
+  return (
+    <Tabs
+      initialRouteName="home"
+      screenOptions={{ headerShown: false }}
+      tabBar={(props) => <BottomTabBar {...props} />}
+    >
+      <Tabs.Screen name="home" options={{ title: "Home" }} />
+      <Tabs.Screen name="learn" options={{ title: "Learn" }} />
+      <Tabs.Screen name="ai-teacher" options={{ title: "AI Teacher" }} />
+      <Tabs.Screen name="chat" options={{ title: "Chat" }} />
+      <Tabs.Screen name="profile" options={{ title: "Profile" }} />
+    </Tabs>
+  );
+}

app/(tabs)/ai-teacher.tsx

@@ -0,0 +1,10 @@
+import { TabPlaceholderScreen } from "@/components/tab-placeholder-screen";
+
+export default function AiTeacherScreen() {
+  return (
+    <TabPlaceholderScreen
+      title="AI Teacher"
+      subtitle="Video teacher sessions will live here."
+    />
+  );
+}

app/(tabs)/chat.tsx

@@ -0,0 +1,10 @@
+import { TabPlaceholderScreen } from "@/components/tab-placeholder-screen";
+
+export default function ChatScreen() {
+  return (
+    <TabPlaceholderScreen
+      title="Chat"
+      subtitle="AI tutor conversations will live here."
+    />
+  );
+}

app/(tabs)/home.tsx

@@ -0,0 +1,10 @@
+import { TabPlaceholderScreen } from "@/components/tab-placeholder-screen";
+
+export default function HomeScreen() {
+  return (
+    <TabPlaceholderScreen
+      title="Home"
+      subtitle="Home content will be implemented in the next step."
+    />
+  );
+}

app/(tabs)/learn.tsx

@@ -0,0 +1,10 @@
+import { TabPlaceholderScreen } from "@/components/tab-placeholder-screen";
+
+export default function LearnScreen() {
+  return (
+    <TabPlaceholderScreen
+      title="Learn"
+      subtitle="Lesson browsing and practice will live here."
+    />
+  );
+}

app/(tabs)/profile.tsx

@@ -0,0 +1,10 @@
+import { TabPlaceholderScreen } from "@/components/tab-placeholder-screen";
+
+export default function ProfileScreen() {
+  return (
+    <TabPlaceholderScreen
+      title="Profile"
+      subtitle="Account details and learning stats will live here."
+    />
+  );
+}

app/language-selection.tsx → app/LanguageSelection.tsx

@@ -1,5 +1,6 @@
 import { images } from "@/constants/images";
 import { defaultLanguageId, languages } from "@/data/languages";
+import { useLanguageStore } from "@/store/UseLanguageStore";
 import type { SupportedLanguage } from "@/types/learning";
 import { Ionicons } from "@expo/vector-icons";
 import { router } from "expo-router";
@@ -19,8 +20,14 @@ import { useSafeAreaInsets } from "react-native-safe-area-context";
 export default function LanguageSelectionScreen() {
   const insets = useSafeAreaInsets();
   const { width } = useWindowDimensions();
+  const persistedLanguageId = useLanguageStore((state) => state.selectedLanguageId);
+  const setSelectedLanguage = useLanguageStore(
+    (state) => state.setSelectedLanguageId,
+  );
   const [searchQuery, setSearchQuery] = useState("");
-  const [selectedLanguageId, setSelectedLanguageId] = useState(defaultLanguageId);
+  const [selectedLanguageId, setSelectedLanguageId] = useState(
+    persistedLanguageId ?? defaultLanguageId,
+  );
   const earthWidth = Math.min(width * 0.95, 520);
   const earthHeight = earthWidth * (828 / 1127);
 
@@ -51,6 +58,15 @@ export default function LanguageSelectionScreen() {
     [selectedLanguageId],
   );
 
+  const handleConfirmLanguage = () => {
+    if (!selectedLanguage) {
+      return;
+    }
+
+    setSelectedLanguage(selectedLanguage.id);
+    router.replace("/");
+  };
+
   return (
     <View className="flex-1 bg-white">
       <ScrollView
@@ -133,6 +149,8 @@ export default function LanguageSelectionScreen() {
         <Pressable
           accessibilityLabel={`Confirm ${selectedLanguage.name}`}
           className="mt-[24px] flex-row items-center justify-center gap-[12px] rounded-[26px] bg-lingua-deep-purple px-[22px] py-[18px]"
+          disabled={!selectedLanguage}
+          onPress={handleConfirmLanguage}
           style={({ pressed }) => [styles.confirmButton, pressed && styles.pressed]}
         >
           <Ionicons name="checkmark-circle" size={26} color="#FFFFFF" />