refactor(diary): Phase 3 质量提升 — 201 状态码 + OpenAPI 文档 + DiaryEvent 类型安全

前端:
- fix(app): Isar native 文件直接导入 isar_database_native.dart，消除 5 个条件导出类型错误
- chore(app): build_runner 重新生成 .g.dart 文件 (102 outputs)
- fix(app): 移除 secure_token_store_factory 未使用的 kIsWeb import

后端:
- refactor(diary): 所有创建端点 POST 返回 201 Created (9 handler, 11 端点)
- feat(diary): DiaryApiDoc OpenApi derive — 42 路径 + 32 Schema 汇总到 Swagger
- feat(diary): DiaryEvent 枚举添加 event_type/payload/to_domain_event 方法 + 4 测试

测试: 84/84 erp-diary 通过, 509/509 全仓库通过, Flutter analyze 0 error

app/lib/data/services/sync_engine_native.dart

@@ -20,7 +20,7 @@ import 'package:connectivity_plus/connectivity_plus.dart';
 import 'package:flutter/foundation.dart';
 import 'package:isar/isar.dart';
 
-import '../local/isar_database.dart';
+import '../local/isar_database_native.dart';
 import '../local/collections/pending_operation_collection.dart';
 import '../remote/api_client.dart';
 
@@ -312,7 +312,7 @@ class SyncEngine {
   /// 在 app 退出、isolate 暂停、或同步完成后调用。
   Future<void> persistPendingQueue() async {
     if (!IsarDatabase.isAvailable) return;
-    final isar = IsarDatabase.instance!;
+    final isar = IsarDatabase.instance;
     final ops = snapshot;
 
     await isar.writeTxn(() async {
@@ -333,7 +333,7 @@ class SyncEngine {
   /// Web 平台上 Isar 不可用，跳过恢复。
   Future<void> restorePendingQueue() async {
     if (!IsarDatabase.isAvailable) return;
-    final isar = IsarDatabase.instance!;
+    final isar = IsarDatabase.instance;
     final persisted = await isar.pendingOperationCollections
         .where()
         .anyIsarId()