feat(core): add AppLogger

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/core/logger.dart

@@ -0,0 +1,18 @@
+import 'package:flutter/foundation.dart';
+
+/// Logger minimal de l'application. Remplace les appels directs à print().
+/// Silencieux en release.
+class AppLogger {
+  AppLogger._();
+
+  static void info(String message) {
+    if (kDebugMode) debugPrint('[INFO] $message');
+  }
+
+  static void error(String message, [Object? error, StackTrace? stackTrace]) {
+    if (kDebugMode) {
+      debugPrint('[ERROR] $message${error != null ? ' : $error' : ''}');
+      if (stackTrace != null) debugPrint(stackTrace.toString());
+    }
+  }
+}