Phase 1 scaffold: auth for all apps

- Backend: Fastify with two listeners (public + internal), routes, services, DB migration + seed
- client_app: Flutter with BLoC, all auth screens (welcome, display name, register, OTP, force-register)
- mitra_app: Flutter with BLoC, OTP-only login
- control_center: React + Vite, email/password login, mitra/user management, anonymity settings
- Docs: phase1 plan, API contract, client app mockup
- CLAUDE.md and shared memory for all subprojects

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

client_app/lib/features/auth/screens/welcome_screen.dart

@@ -0,0 +1,44 @@
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+
+class WelcomeScreen extends StatelessWidget {
+  const WelcomeScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: SafeArea(
+        child: Padding(
+          padding: const EdgeInsets.all(24),
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            crossAxisAlignment: CrossAxisAlignment.stretch,
+            children: [
+              const Text(
+                'Halo Bestie',
+                style: TextStyle(fontSize: 32, fontWeight: FontWeight.bold),
+                textAlign: TextAlign.center,
+              ),
+              const SizedBox(height: 8),
+              const Text(
+                'Tempat curhat kamu',
+                style: TextStyle(fontSize: 16, color: Colors.grey),
+                textAlign: TextAlign.center,
+              ),
+              const SizedBox(height: 48),
+              ElevatedButton(
+                onPressed: () => context.push('/auth/display-name'),
+                child: const Text('Lanjut sebagai Tamu'),
+              ),
+              const SizedBox(height: 12),
+              OutlinedButton(
+                onPressed: () => context.push('/auth/register'),
+                child: const Text('Daftar / Masuk'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}