feat(app): 添加 EditorBloc.LoadJournal event — 加载已有日记数据

- LoadJournal event: 原子加载 title/mood/tags/strokes/elements/lastSavedAt
- _onLoadJournal handler: 不触发 auto-save (isDirty=false)
- 单元测试: 验证 LoadJournal 正确还原所有状态字段
- mood_bloc: linter 补充 foundation.dart import

app/test/features/editor/bloc/editor_bloc_test.dart

@@ -6,6 +6,7 @@
 import 'dart:math';
 
 import 'package:flutter_test/flutter_test.dart';
+import 'package:nuanji_app/data/models/journal_entry.dart';
 import 'package:nuanji_app/data/models/journal_element.dart';
 import 'package:nuanji_app/features/editor/bloc/editor_bloc.dart';
 import 'package:nuanji_app/features/editor/widgets/stroke_model.dart';
@@ -262,5 +263,35 @@ void main() {
 
       bloc.close();
     });
+
+    // ===== LoadJournal 原子加载 =====
+
+    test('LoadJournal 还原已有日记数据', () async {
+      final strokes = [_testStroke(id: 's1')];
+      final elements = [
+        JournalElement.createSticker(
+          journalId: 'j1',
+          emoji: '😊',
+          position: Offset.zero,
+        ),
+      ];
+
+      final state = await dispatch(LoadJournal(
+        title: '测试日记',
+        mood: Mood.happy,
+        tags: const ['开心', '学校'],
+        strokes: strokes,
+        elements: elements,
+        lastSavedAt: DateTime(2026, 6, 1),
+      ));
+
+      expect(state.title, '测试日记');
+      expect(state.selectedMood, Mood.happy);
+      expect(state.tags, ['开心', '学校']);
+      expect(state.strokes.length, 1);
+      expect(state.elements.length, 1);
+      expect(state.lastSavedAt, DateTime(2026, 6, 1));
+      expect(state.isDirty, isFalse, reason: 'LoadJournal 不应标记为 dirty');
+    });
   });
 }