feat(app): 添加 JournalElement 类型便利工厂方法 — text/image/sticker

app/lib/data/models/journal_element.dart

@@ -1,6 +1,7 @@
 // 日记元素数据模型 — 手写不可变类（避免 build_runner 依赖）
 
 import 'dart:collection';
+import 'dart:ui';
 
 import 'package:uuid/uuid.dart';
 
@@ -153,4 +154,65 @@ class JournalElement {
       updatedAt: now,
     );
   }
+
+  /// 文字元素便利工厂
+  factory JournalElement.createText({
+    required String journalId,
+    required String text,
+    required Offset position,
+    double fontSize = 18.0,
+    String fontColor = '#2D2420',
+  }) {
+    return JournalElement.create(
+      journalId: journalId,
+      elementType: ElementType.text,
+      positionX: position.dx,
+      positionY: position.dy,
+      content: {
+        'text': text,
+        'fontSize': fontSize,
+        'fontColor': fontColor,
+      },
+    );
+  }
+
+  /// 图片元素便利工厂
+  factory JournalElement.createImage({
+    required String journalId,
+    required String filePath,
+    required Offset position,
+    String? thumbnailPath,
+  }) {
+    return JournalElement.create(
+      journalId: journalId,
+      elementType: ElementType.image,
+      positionX: position.dx,
+      positionY: position.dy,
+      content: {
+        'filePath': filePath,
+        if (thumbnailPath != null) 'thumbnailPath': thumbnailPath,
+      },
+    );
+  }
+
+  /// 贴纸元素便利工厂
+  factory JournalElement.createSticker({
+    required String journalId,
+    required String emoji,
+    required Offset position,
+    String? stickerPackId,
+    String? stickerId,
+  }) {
+    return JournalElement.create(
+      journalId: journalId,
+      elementType: ElementType.sticker,
+      positionX: position.dx,
+      positionY: position.dy,
+      content: {
+        'emoji': emoji,
+        if (stickerPackId != null) 'stickerPackId': stickerPackId,
+        if (stickerId != null) 'stickerId': stickerId,
+      },
+    );
+  }
 }