refactor(core): keep logger pure-Dart and document Result subtypes

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

lib/core/logger.dart

@@ -1,18 +1,21 @@
-import 'package:flutter/foundation.dart';
+import 'dart:developer' as dev;
 
 /// Logger minimal de l'application. Remplace les appels directs à print().
-/// Silencieux en release.
+/// Silencieux en release (les blocs assert sont retirés du build release).
 class AppLogger {
   AppLogger._();
 
   static void info(String message) {
-    if (kDebugMode) debugPrint('[INFO] $message');
+    assert(() {
+      dev.log(message, name: 'INFO');
+      return true;
+    }());
   }
 
   static void error(String message, [Object? error, StackTrace? stackTrace]) {
-    if (kDebugMode) {
-      debugPrint('[ERROR] $message${error != null ? ' : $error' : ''}');
-      if (stackTrace != null) debugPrint(stackTrace.toString());
-    }
+    assert(() {
+      dev.log(message, name: 'ERROR', error: error, stackTrace: stackTrace);
+      return true;
+    }());
   }
 }

lib/core/result.dart

@@ -3,11 +3,13 @@ sealed class Result<T> {
   const Result();
 }
 
+/// Issue réussie, encapsule [value].
 class Success<T> extends Result<T> {
   final T value;
   const Success(this.value);
 }
 
+/// Issue en échec, encapsule [error] et une [stackTrace] optionnelle.
 class Failure<T> extends Result<T> {
   final Object error;
   final StackTrace? stackTrace;