로그 포맷 통일, slog 적용

frontend/lib/core/services/auth_proxy_service.dart

@@ -99,19 +99,28 @@ class AuthProxyService {
     }
   }
 
-  static Future<void> logError(String message) async {
+  static Future<void> sendLog(String level, String message, {Map<String, dynamic>? data}) async {
     final url = Uri.parse('$_baseUrl/api/v1/client-log');
     try {
       await http.post(
         url,
         headers: {'Content-Type': 'application/json'},
         body: jsonEncode({
-          'level': 'ERROR',
+          'level': level,
           'message': message,
+          if (data != null) 'data': data,
         }),
       );
     } catch (_) {
       // Ignore logging errors to prevent loops
     }
   }
+
+  static Future<void> logError(String message, {dynamic error, StackTrace? stackTrace}) async {
+    final data = <String, dynamic>{};
+    if (error != null) data['error'] = error.toString();
+    if (stackTrace != null) data['stack'] = stackTrace.toString();
+    
+    await sendLog('ERROR', message, data: data);
+  }
 }

frontend/lib/core/services/logger_service.dart

@@ -0,0 +1,86 @@
+import 'dart:convert';
+import 'package:flutter/foundation.dart';
+import 'package:logging/logging.dart' as std_log;
+import 'package:logger/logger.dart' as pretty_log;
+import 'auth_proxy_service.dart';
+
+/// Global Logger Service for Baron SSO Frontend
+class LoggerService {
+  static final LoggerService _instance = LoggerService._internal();
+  factory LoggerService() => _instance;
+
+  late final pretty_log.Logger _prettyLogger;
+
+  LoggerService._internal() {
+    // 1. Initialize Pretty Logger for Dev
+    _prettyLogger = pretty_log.Logger(
+      printer: pretty_log.PrettyPrinter(
+        methodCount: 0,
+        errorMethodCount: 8,
+        lineLength: 120,
+        colors: true,
+        printEmojis: true,
+        dateTimeFormat: pretty_log.DateTimeFormat.onlyTimeAndSinceStart,
+      ),
+    );
+
+    // 2. Configure Standard Logger (logging package)
+    std_log.Logger.root.level = kReleaseMode ? std_log.Level.INFO : std_log.Level.ALL;
+    
+    std_log.Logger.root.onRecord.listen((record) {
+      if (kReleaseMode) {
+        // [Production] Log as JSON
+        _logJson(record);
+      } else {
+        // [Development] Log using Pretty Printer
+        _logPretty(record);
+      }
+    });
+  }
+
+  /// Initialize the logger. Call this in main.dart
+  static void init() {
+    // Accessing the instance triggers the constructor
+    LoggerService(); 
+    std_log.Logger('BaronSSO').info('Logger initialized');
+  }
+
+  void _logPretty(std_log.LogRecord record) {
+    if (record.level >= std_log.Level.SEVERE) {
+      _prettyLogger.e(record.message, error: record.error, stackTrace: record.stackTrace);
+    } else if (record.level >= std_log.Level.WARNING) {
+      _prettyLogger.w(record.message);
+    } else if (record.level >= std_log.Level.INFO) {
+      _prettyLogger.i(record.message);
+    } else {
+      _prettyLogger.d(record.message);
+    }
+  }
+
+  void _logJson(std_log.LogRecord record) {
+    final logData = {
+      'time': record.time.toUtc().toIso8601String(), // Use UTC for consistency
+      'level': record.level.name,
+      'msg': record.message,
+      'svc': 'baron-frontend',
+      if (record.error != null) 'error': record.error.toString(),
+      if (record.stackTrace != null) 'stack': record.stackTrace.toString(),
+    };
+    
+    // 1. Print to Browser Console (F12)
+    debugPrint(jsonEncode(logData));
+
+    // 2. Relay to Backend (Docker Terminal)
+    if (record.level >= std_log.Level.INFO) {
+      AuthProxyService.sendLog(
+        record.level.name,
+        record.message,
+        data: {
+          'client_time': record.time.toUtc().toIso8601String(),
+          'logger': record.loggerName,
+          if (record.error != null) 'error': record.error.toString(),
+        },
+      );
+    }
+  }
+}