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>

mitra_app/lib/features/splash/splash_screen.dart

@@ -5,20 +5,12 @@ class SplashScreen extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return const Scaffold(
+    return Scaffold(
+      backgroundColor: Colors.white,
       body: Center(
-        child: Column(
-          mainAxisAlignment: MainAxisAlignment.center,
-          children: [
-            Icon(Icons.favorite, size: 80, color: Colors.blue),
-            SizedBox(height: 24),
-            Text(
-              'Halo Bestie Mitra',
-              style: TextStyle(fontSize: 28, fontWeight: FontWeight.bold),
-            ),
-            SizedBox(height: 32),
-            CircularProgressIndicator(),
-          ],
+        child: Image.asset(
+          'assets/images/splash_chat_hebat.png',
+          width: 200,
         ),
       ),
     );