Chat UI redesign, splash screen, and onboarding carousel

- Redesign chat screens (both apps) to match Figma: pink theme with
  doodle pattern background, white app bar with centered name and
  chevron back, rose sender bubbles, white receiver bubbles, entry
  banners, and session-ended bottom bar
- Add splash_chat_hebat.png as native Android splash screen with
  Android 12+ support (values-v31)
- Add Flutter splash screen using splash_chat_hebat.png
- Add onboarding carousel (client_app only): 3 pages with 1s
  auto-advance, last page manual "Mulai" button, first-launch only
- Register image assets in both pubspec.yaml files

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

client_app/lib/router.dart

@@ -8,6 +8,7 @@ import 'features/auth/screens/register_screen.dart';
 import 'features/auth/screens/otp_screen.dart';
 import 'features/auth/screens/force_register_screen.dart';
 import 'features/auth/screens/set_display_name_screen.dart';
+import 'features/onboarding/onboarding_screen.dart';
 import 'features/splash/splash_screen.dart';
 import 'features/home/home_screen.dart';
 import 'features/chat/screens/searching_screen.dart';
@@ -25,6 +26,9 @@ class RouterNotifier extends ChangeNotifier {
   }
 }
 
+/// Cached onboarding status — loaded once at startup, invalidated after onboarding completes
+final onboardingDoneProvider = FutureProvider<bool>((ref) => isOnboardingDone());
+
 final routerProvider = Provider<GoRouter>((ref) => buildRouter(ref));
 
 GoRouter buildRouter(Ref ref) {
@@ -36,15 +40,25 @@ GoRouter buildRouter(Ref ref) {
     redirect: (context, state) {
       final authState = ref.read(authProvider);
       final isSplash = state.matchedLocation == '/splash';
+      final isOnboarding = state.matchedLocation == '/onboarding';
       final isAuthRoute = state.matchedLocation.startsWith('/auth') ||
           state.matchedLocation == '/welcome';
 
-      // Show splash only during initial load — don't redirect away from auth routes
+      // Show splash only during initial load
       if (authState is AsyncLoading) {
-        if (isSplash || isAuthRoute) return null;
+        if (isSplash || isAuthRoute || isOnboarding) return null;
         return '/splash';
       }
 
+      // Check onboarding status — must complete before anything else
+      final onboardingDone = ref.read(onboardingDoneProvider).valueOrNull ?? false;
+      if (!onboardingDone) {
+        return isOnboarding ? null : '/onboarding';
+      }
+      if (isOnboarding) {
+        return '/welcome';
+      }
+
       final data = authState.valueOrNull;
       if (data == null) {
         // Error state — show login
@@ -64,6 +78,7 @@ GoRouter buildRouter(Ref ref) {
     },
     routes: [
       GoRoute(path: '/splash', builder: (_, __) => const SplashScreen()),
+      GoRoute(path: '/onboarding', builder: (_, __) => const OnboardingScreen()),
       GoRoute(path: '/welcome', builder: (_, __) => const WelcomeScreen()),
       GoRoute(path: '/auth/display-name', builder: (_, __) => const DisplayNameScreen()),
       GoRoute(path: '/auth/register', builder: (_, __) => const RegisterScreen()),