feat(client): Dio 拦截器统一上报 5xx 错误，新增 api_error 类型

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/core/api/api_client.dart

@@ -3,6 +3,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import '../auth/auth_state.dart';
 import '../config/app_config.dart';
+import '../errors/error_reporter.dart';
 import '../../providers/connectivity_provider.dart';
 
 /// Public Dio instance for unauthenticated calls (login / refresh)
@@ -74,6 +75,16 @@ class ApiClient {
             return handler.next(e);
           }
 
+          // 服务端 5xx 错误上报（4xx 是业务/权限错误，不上报）
+          final statusCode = e.response?.statusCode ?? 0;
+          if (statusCode >= 500) {
+            reportError(
+              '[${e.requestOptions.method}] ${e.requestOptions.path} → $statusCode',
+              e.stackTrace,
+              errorType: ErrorType.apiError,
+            );
+          }
+
           if (e.response?.statusCode == 401 && (refreshToken ?? '').isNotEmpty) {
             debugPrint('[ApiClient] got 401 on ${e.requestOptions.path}, trying refresh...');
             try {

client/lib/core/errors/error_reporter.dart

@@ -12,6 +12,7 @@ class ErrorType {
   static const flutterError = 'flutter_error';
   static const zoneError = 'zone_error';
   static const caughtException = 'caught_exception';
+  static const apiError = 'api_error';
 }
 
 class ErrorReporter {