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>

mitra_app/lib/core/chat/chat_request_notifier.dart

@@ -54,6 +54,8 @@ class ChatRequest extends _$ChatRequest {
   ChatRequestData build() => const ChatRequestIdleData();
 
   Future<void> startListening() async {
+    // Don't reset state if actively accepting/accepted — would lose navigation
+    if (state is ChatRequestAcceptingData || state is ChatRequestAcceptedData) return;
     _closeWebSocket();
     state = const ChatRequestListeningData();
     await _connectWebSocket();