feat(app): Isar 本地数据库集成 — Collection + Repository + 编辑器持久化 + SyncEngine 队列

新增文件:
- data/local/collections/ 3 个 Isar Collection 定义 + 生成 Schema
- data/repositories/isar_journal_repository.dart 完整 CRUD + 乐观锁

修改文件:
- app.dart: IsarJournalRepository 注册为主 JournalRepository + SyncEngine 注入
- editor_page.dart: onSave 接入 JournalRepository，笔画/元素自动保存到 Isar
- sync_engine.dart: 新增 persistPendingQueue/restorePendingQueue Isar 持久化
- isar_database.dart: 注册 3 个 Collection Schema
- main.dart: 启动时初始化 Isar

架构: 离线优先 — Isar 为本地主仓库，Remote 供 SyncEngine 推送

app/lib/features/editor/views/editor_page.dart

@@ -15,8 +15,11 @@ import 'package:go_router/go_router.dart';
 
 import '../../../core/constants/design_tokens.dart';
 import '../../../data/models/journal_element.dart';
+import '../../../data/models/journal_entry.dart';
+import '../../../data/repositories/journal_repository.dart';
 import '../bloc/editor_bloc.dart';
 import '../widgets/handwriting_canvas.dart';
+import '../widgets/stroke_model.dart';
 import '../widgets/draggable_element.dart';
 import '../widgets/editor_toolbar.dart';
 
@@ -28,22 +31,123 @@ class EditorPage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    // 从 Provider 树获取 JournalRepository（IsarJournalRepository）
+    final repo = context.read<JournalRepository>();
+
+    // 可变闭包变量：跟踪已保存的日记 ID
+    // 新建日记首次保存后赋值，后续自动更新使用此 ID
+    String? savedJournalId = journalId;
+
     return BlocProvider(
       create: (_) => EditorBloc(
-        onSave: (state) {
-          // TODO: 通过 JournalRepository 保存到 Isar
-          debugPrint('自动保存: ${state.strokes.length} 笔画, ${state.elements.length} 元素');
+        onSave: (state) async {
+          try {
+            await _persistState(repo, state, (id) => savedJournalId = id, savedJournalId);
+          } catch (e) {
+            debugPrint('自动保存失败: $e');
+          }
         },
       ),
-      child: _EditorView(journalId: journalId),
+      child: _EditorView(
+        journalId: journalId,
+        onSaveComplete: () => context.pop(),
+      ),
     );
   }
+
+  /// 持久化编辑器状态到 Isar
+  ///
+  /// 策略：
+  /// - 首次保存（savedJournalId == null）→ createJournal + addElement
+  /// - 后续保存 → updateJournal + upsert 元素
+  /// - 笔画序列化为 handwriting_ref 元素
+  Future<void> _persistState(
+    JournalRepository repo,
+    EditorState state,
+    void Function(String) setId,
+    String? savedJournalId,
+  ) async {
+    final now = DateTime.now();
+
+    if (savedJournalId == null) {
+      // --- 新建日记 ---
+      final entry = JournalEntry.create(
+        authorId: 'local', // TODO: 从 AuthBloc 获取真实用户 ID
+        title: '${now.month}月${now.day}日的日记',
+        date: now,
+      );
+      await repo.createJournal(entry);
+      setId(entry.id);
+
+      // 保存笔画
+      if (state.strokes.isNotEmpty) {
+        await _saveStrokesAsElement(repo, entry.id, state.strokes);
+      }
+
+      // 保存其他元素
+      for (final element in state.elements) {
+        await repo.addElement(element.copyWith(journalId: entry.id));
+      }
+    } else {
+      // --- 更新已有日记 ---
+      final existing = await repo.getJournal(savedJournalId);
+      if (existing != null) {
+        await repo.updateJournal(existing);
+      }
+
+      // 更新笔画
+      if (state.strokes.isNotEmpty) {
+        await _saveStrokesAsElement(repo, savedJournalId, state.strokes);
+      }
+
+      // upsert 元素（先尝试更新，失败则新建）
+      for (final element in state.elements) {
+        try {
+          await repo.updateElement(element);
+        } catch (_) {
+          await repo.addElement(element);
+        }
+      }
+    }
+  }
+
+  /// 将笔画列表序列化为 handwriting_ref 元素并保存
+  ///
+  /// 每次保存都替换整个笔画集（Phase 1 简化策略）。
+  Future<void> _saveStrokesAsElement(
+    JournalRepository repo,
+    String journalId,
+    List<Stroke> strokes,
+  ) async {
+    final now = DateTime.now();
+    final strokesJson = strokes.map((s) => s.toJson()).toList();
+
+    final element = JournalElement(
+      id: '${journalId}_strokes', // 固定 ID，保证每次覆盖
+      journalId: journalId,
+      elementType: ElementType.handwritingRef,
+      content: {
+        'strokes': strokesJson,
+        'strokeCount': strokes.length,
+      },
+      version: 1,
+      createdAt: now,
+      updatedAt: now,
+    );
+
+    try {
+      await repo.updateElement(element);
+    } catch (_) {
+      await repo.addElement(element);
+    }
+  }
 }
 
 class _EditorView extends StatelessWidget {
   final String? journalId;
+  final VoidCallback onSaveComplete;
 
-  const _EditorView({this.journalId});
+  const _EditorView({this.journalId, required this.onSaveComplete});
 
   @override
   Widget build(BuildContext context) {
@@ -117,10 +221,7 @@ class _EditorView extends StatelessWidget {
 
           // 完成按钮
           FilledButton.tonal(
-            onPressed: () {
-              // TODO: 保存并返回
-              context.pop();
-            },
+            onPressed: onSaveComplete,
             style: FilledButton.styleFrom(
               padding: const EdgeInsets.symmetric(horizontal: DesignTokens.spacing16),
               minimumSize: const Size(0, 36),