feat(app): 统一同步协议 — SyncModels + ApiClient.sync + SyncEngine.tryBatchSync

Flutter ↔ Rust 同步协议对齐:
- 新增 sync_models.dart: SyncReq/SyncResp/SyncChange/ConflictInfo
  与 Rust dto.rs 一一对应 (CreateJournal/UpdateJournal/DeleteJournal)
- ApiClient.sync(): 调用 POST /diary/sync 批量同步端点
- SyncEngine.tryBatchSync(): PendingOperation → SyncChange 批量提交
  成功清空队列，冲突保留待用户处理

保留原有逐个同步 trySync() 作为降级方案
后端 509/509 测试通过, Flutter analyze 0 error

app/lib/data/models/sync_models.dart

@@ -0,0 +1,176 @@
+// 同步协议模型 — 与 Rust 端 SyncReq/SyncResp/SyncChange/ConflictInfo 一一对应
+//
+// 端点: POST /api/v1/diary/sync
+// Rust DTO: crates/erp-diary/src/dto.rs (SyncReq, SyncResp, SyncChange, ConflictInfo)
+
+/// 同步请求 — 与 Rust SyncReq 对应
+///
+/// ```rust
+/// pub struct SyncReq {
+///     pub last_sync_time: Option<DateTime<Utc>>,
+///     pub changes: Vec<SyncChange>,
+/// }
+/// ```
+class SyncReq {
+  final DateTime? lastSyncTime;
+  final List<SyncChange> changes;
+
+  const SyncReq({this.lastSyncTime, this.changes = const []});
+
+  Map<String, dynamic> toJson() => {
+        if (lastSyncTime != null)
+          'last_sync_time': lastSyncTime!.toUtc().toIso8601String(),
+        'changes': changes.map((c) => c.toJson()).toList(),
+      };
+}
+
+/// 同步变更条目 — 与 Rust SyncChange 枚举对应
+///
+/// ```rust
+/// pub enum SyncChange {
+///     CreateJournal { data: serde_json::Value },
+///     UpdateJournal { id: Uuid, version: i32, data: serde_json::Value },
+///     DeleteJournal { id: Uuid, version: i32 },
+/// }
+/// ```
+sealed class SyncChange {
+  const SyncChange();
+
+  Map<String, dynamic> toJson();
+
+  /// 从 JSON 反序列化
+  factory SyncChange.fromJson(Map<String, dynamic> json) {
+    if (json.containsKey('CreateJournal')) {
+      return SyncChangeCreateJournal(
+        data: json['CreateJournal']['data'] as Map<String, dynamic>,
+      );
+    }
+    if (json.containsKey('UpdateJournal')) {
+      final inner = json['UpdateJournal'] as Map<String, dynamic>;
+      return SyncChangeUpdateJournal(
+        id: inner['id'] as String,
+        version: inner['version'] as int,
+        data: inner['data'] as Map<String, dynamic>,
+      );
+    }
+    if (json.containsKey('DeleteJournal')) {
+      final inner = json['DeleteJournal'] as Map<String, dynamic>;
+      return SyncChangeDeleteJournal(
+        id: inner['id'] as String,
+        version: inner['version'] as int,
+      );
+    }
+    throw FormatException('Unknown SyncChange variant: $json');
+  }
+}
+
+/// 创建日记变更
+class SyncChangeCreateJournal extends SyncChange {
+  final Map<String, dynamic> data;
+
+  const SyncChangeCreateJournal({required this.data});
+
+  @override
+  Map<String, dynamic> toJson() => {
+        'CreateJournal': {'data': data},
+      };
+}
+
+/// 更新日记变更
+class SyncChangeUpdateJournal extends SyncChange {
+  final String id;
+  final int version;
+  final Map<String, dynamic> data;
+
+  const SyncChangeUpdateJournal({
+    required this.id,
+    required this.version,
+    required this.data,
+  });
+
+  @override
+  Map<String, dynamic> toJson() => {
+        'UpdateJournal': {
+          'id': id,
+          'version': version,
+          'data': data,
+        },
+      };
+}
+
+/// 删除日记变更
+class SyncChangeDeleteJournal extends SyncChange {
+  final String id;
+  final int version;
+
+  const SyncChangeDeleteJournal({
+    required this.id,
+    required this.version,
+  });
+
+  @override
+  Map<String, dynamic> toJson() => {
+        'DeleteJournal': {
+          'id': id,
+          'version': version,
+        },
+      };
+}
+
+/// 同步响应 — 与 Rust SyncResp 对应
+///
+/// ```rust
+/// pub struct SyncResp {
+///     pub server_changes: Vec<serde_json::Value>,
+///     pub conflicts: Vec<ConflictInfo>,
+///     pub sync_time: DateTime<Utc>,
+/// }
+/// ```
+class SyncResp {
+  final List<Map<String, dynamic>> serverChanges;
+  final List<ConflictInfo> conflicts;
+  final DateTime syncTime;
+
+  const SyncResp({
+    required this.serverChanges,
+    required this.conflicts,
+    required this.syncTime,
+  });
+
+  factory SyncResp.fromJson(Map<String, dynamic> json) => SyncResp(
+        serverChanges: (json['server_changes'] as List)
+            .map((e) => Map<String, dynamic>.from(e as Map))
+            .toList(),
+        conflicts: (json['conflicts'] as List)
+            .map((e) => ConflictInfo.fromJson(Map<String, dynamic>.from(e as Map)))
+            .toList(),
+        syncTime: DateTime.parse(json['sync_time'] as String),
+      );
+}
+
+/// 冲突信息 — 与 Rust ConflictInfo 对应
+///
+/// ```rust
+/// pub struct ConflictInfo {
+///     pub journal_id: Uuid,
+///     pub local_version: i32,
+///     pub server_version: i32,
+/// }
+/// ```
+class ConflictInfo {
+  final String journalId;
+  final int localVersion;
+  final int serverVersion;
+
+  const ConflictInfo({
+    required this.journalId,
+    required this.localVersion,
+    required this.serverVersion,
+  });
+
+  factory ConflictInfo.fromJson(Map<String, dynamic> json) => ConflictInfo(
+        journalId: json['journal_id'] as String,
+        localVersion: json['local_version'] as int,
+        serverVersion: json['server_version'] as int,
+      );
+}

app/lib/data/remote/api_client.dart

@@ -10,6 +10,8 @@
 import 'package:dio/dio.dart';
 import 'package:connectivity_plus/connectivity_plus.dart';
 
+import '../models/sync_models.dart';
+
 /// 网络离线异常 — 网络不可用时由 ApiClient 抛出
 class OfflineException implements Exception {
   final String message;
@@ -187,4 +189,19 @@ class ApiClient {
     });
     return _dio.post<T>(path, data: formData);
   }
+
+  // ===== 同步 API =====
+
+  /// 批量同步 — POST /diary/sync
+  ///
+  /// 将客户端变更批量提交到服务端，返回服务端变更和冲突信息。
+  /// 对应 Rust sync_handler::sync_journals 端点。
+  Future<SyncResp> sync(SyncReq req) async {
+    await _ensureOnline();
+    final response = await _dio.post<Map<String, dynamic>>(
+      '/diary/sync',
+      data: req.toJson(),
+    );
+    return SyncResp.fromJson(response.data!);
+  }
 }

app/lib/data/services/sync_engine_native.dart

@@ -22,6 +22,7 @@ import 'package:isar/isar.dart';
 
 import '../local/isar_database_native.dart';
 import '../local/collections/pending_operation_collection.dart';
+import '../models/sync_models.dart';
 import '../remote/api_client.dart';
 
 /// 同步操作类型
@@ -277,6 +278,79 @@ class SyncEngine {
     await persistPendingQueue();
   }
 
+  /// 批量同步 — 使用 POST /diary/sync 端点一次性提交所有变更
+  ///
+  /// 将队列中的 PendingOperation 转换为 SyncChange 列表，
+  /// 调用 Rust sync_handler 批量处理，获取服务端变更和冲突。
+  /// 成功后清空队列；失败时保留队列供重试。
+  Future<SyncResp?> tryBatchSync({DateTime? lastSyncTime}) async {
+    if (_status == SyncStatus.syncing) return null;
+    if (_pendingQueue.isEmpty) {
+      _status = SyncStatus.idle;
+      return null;
+    }
+
+    _status = SyncStatus.syncing;
+    _lastError = null;
+
+    try {
+      // 转换: PendingOperation → SyncChange
+      final changes = _pendingQueue.map(_operationToSyncChange).toList();
+
+      final req = SyncReq(
+        lastSyncTime: lastSyncTime,
+        changes: changes,
+      );
+
+      final resp = await _apiClient.sync(req);
+
+      // 处理冲突 — 将冲突的操作保留在队列中
+      if (resp.conflicts.isNotEmpty) {
+        final conflictIds = resp.conflicts.map((c) => c.journalId).toSet();
+        // 移除已成功同步的非冲突操作，保留冲突操作
+        _pendingQueue.removeWhere(
+          (op) => !conflictIds.contains(op.id),
+        );
+        _lastError = '${resp.conflicts.length} 个操作存在版本冲突';
+      } else {
+        // 全部成功，清空队列
+        _pendingQueue.clear();
+      }
+
+      _status = _pendingQueue.isEmpty ? SyncStatus.idle : SyncStatus.paused;
+      await persistPendingQueue();
+
+      return resp;
+    } on OfflineException {
+      _status = SyncStatus.paused;
+      _lastError = '同步中断：网络不可用';
+      return null;
+    } catch (e) {
+      _status = SyncStatus.error;
+      _lastError = '批量同步失败: $e';
+      return null;
+    }
+  }
+
+  /// PendingOperation → SyncChange 转换
+  SyncChange _operationToSyncChange(PendingOperation op) {
+    switch (op.type) {
+      case SyncOperationType.create:
+        return SyncChangeCreateJournal(data: op.data);
+      case SyncOperationType.update:
+        return SyncChangeUpdateJournal(
+          id: op.id,
+          version: op.version,
+          data: op.data,
+        );
+      case SyncOperationType.delete:
+        return SyncChangeDeleteJournal(
+          id: op.id,
+          version: op.version,
+        );
+    }
+  }
+
   /// 执行单个同步操作
   Future<void> _executeOperation(PendingOperation operation) async {
     switch (operation.type) {