feat: production-ready UI with onboarding wizard and dashboard

- Onboarding flow (welcome -> Codex setup -> Claude setup -> done) with
  dark-themed screens and step indicators; completion stored in SecureStore
- Smart root redirect checks onboarding state on launch
- Dashboard tab shows both services at a glance via ServiceStatusCard;
  useFocusEffect + reload() keeps it fresh when credentials change in tabs
- Settings tab manages credentials and exposes re-run setup wizard
- Polished Codex and Claude detail screens with service headers and empty states
- 4-tab layout (Home, Codex, Claude, Settings) with dark-mode tab bar
- Both hooks gain reload() for cross-tab credential refresh

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/index.tsx

@@ -1,5 +1,18 @@
-import { Redirect } from "expo-router";
+import { useEffect } from "react";
+import { View, ActivityIndicator } from "react-native";
+import { router } from "expo-router";
+import { hasCompletedOnboarding } from "@/lib/setupState";
 
 export default function Index() {
-  return <Redirect href="/(tabs)/codex" />;
+  useEffect(() => {
+    hasCompletedOnboarding().then((done) => {
+      router.replace(done ? "/(tabs)" : "/onboarding");
+    });
+  }, []);
+
+  return (
+    <View className="flex-1 bg-neutral-950 items-center justify-center">
+      <ActivityIndicator color="#10a37f" size="large" />
+    </View>
+  );
 }