Fix auth: auto-create customer, display name flow, OTP auto-verify

- Backend: getOrCreateCustomer with phone fallback for re-login
- Backend: PATCH /api/client/auth/profile for display name update
- Client app: AuthNeedsDisplayNameData state + SetDisplayNameScreen
- Client app: ApiClient.patch method
- Both apps: handle verificationCompleted for auto-verify (test numbers)
- Both apps: skip credential sign-in if already auto-verified
- Remove debug prints from mitra auth + OTP screens
- Fix ChatRequestNotifier.startListening skips when accepting

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

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

@@ -0,0 +1,68 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../../../core/auth/auth_notifier.dart';
+
+class SetDisplayNameScreen extends ConsumerStatefulWidget {
+  const SetDisplayNameScreen({super.key});
+
+  @override
+  ConsumerState<SetDisplayNameScreen> createState() => _SetDisplayNameScreenState();
+}
+
+class _SetDisplayNameScreenState extends ConsumerState<SetDisplayNameScreen> {
+  final _controller = TextEditingController();
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
+  void _submit() {
+    final name = _controller.text.trim();
+    if (name.isEmpty) return;
+    ref.read(authProvider.notifier).setDisplayName(name);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final authState = ref.watch(authProvider);
+    final isLoading = authState is AsyncLoading;
+
+    ref.listen(authProvider, (prev, next) {
+      if (next is AsyncError) {
+        ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text(next.error.toString())));
+      }
+    });
+
+    return Scaffold(
+      appBar: AppBar(title: const Text('Siapa namamu?')),
+      body: Padding(
+        padding: const EdgeInsets.all(24),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.stretch,
+          children: [
+            const Text('Pilih nama yang ingin kamu gunakan. Nama ini akan terlihat oleh Bestie kamu.'),
+            const SizedBox(height: 24),
+            TextField(
+              controller: _controller,
+              decoration: const InputDecoration(
+                labelText: 'Nama panggilan',
+                border: OutlineInputBorder(),
+              ),
+              textInputAction: TextInputAction.done,
+              onSubmitted: (_) => _submit(),
+            ),
+            const SizedBox(height: 24),
+            ElevatedButton(
+              onPressed: isLoading ? null : _submit,
+              child: isLoading
+                  ? const CircularProgressIndicator()
+                  : const Text('Lanjut'),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}